cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
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fs-writeback.c (80669B)


      1// SPDX-License-Identifier: GPL-2.0-only
      2/*
      3 * fs/fs-writeback.c
      4 *
      5 * Copyright (C) 2002, Linus Torvalds.
      6 *
      7 * Contains all the functions related to writing back and waiting
      8 * upon dirty inodes against superblocks, and writing back dirty
      9 * pages against inodes.  ie: data writeback.  Writeout of the
     10 * inode itself is not handled here.
     11 *
     12 * 10Apr2002	Andrew Morton
     13 *		Split out of fs/inode.c
     14 *		Additions for address_space-based writeback
     15 */
     16
     17#include <linux/kernel.h>
     18#include <linux/export.h>
     19#include <linux/spinlock.h>
     20#include <linux/slab.h>
     21#include <linux/sched.h>
     22#include <linux/fs.h>
     23#include <linux/mm.h>
     24#include <linux/pagemap.h>
     25#include <linux/kthread.h>
     26#include <linux/writeback.h>
     27#include <linux/blkdev.h>
     28#include <linux/backing-dev.h>
     29#include <linux/tracepoint.h>
     30#include <linux/device.h>
     31#include <linux/memcontrol.h>
     32#include "internal.h"
     33
     34/*
     35 * 4MB minimal write chunk size
     36 */
     37#define MIN_WRITEBACK_PAGES	(4096UL >> (PAGE_SHIFT - 10))
     38
     39/*
     40 * Passed into wb_writeback(), essentially a subset of writeback_control
     41 */
     42struct wb_writeback_work {
     43	long nr_pages;
     44	struct super_block *sb;
     45	enum writeback_sync_modes sync_mode;
     46	unsigned int tagged_writepages:1;
     47	unsigned int for_kupdate:1;
     48	unsigned int range_cyclic:1;
     49	unsigned int for_background:1;
     50	unsigned int for_sync:1;	/* sync(2) WB_SYNC_ALL writeback */
     51	unsigned int auto_free:1;	/* free on completion */
     52	enum wb_reason reason;		/* why was writeback initiated? */
     53
     54	struct list_head list;		/* pending work list */
     55	struct wb_completion *done;	/* set if the caller waits */
     56};
     57
     58/*
     59 * If an inode is constantly having its pages dirtied, but then the
     60 * updates stop dirtytime_expire_interval seconds in the past, it's
     61 * possible for the worst case time between when an inode has its
     62 * timestamps updated and when they finally get written out to be two
     63 * dirtytime_expire_intervals.  We set the default to 12 hours (in
     64 * seconds), which means most of the time inodes will have their
     65 * timestamps written to disk after 12 hours, but in the worst case a
     66 * few inodes might not their timestamps updated for 24 hours.
     67 */
     68unsigned int dirtytime_expire_interval = 12 * 60 * 60;
     69
     70static inline struct inode *wb_inode(struct list_head *head)
     71{
     72	return list_entry(head, struct inode, i_io_list);
     73}
     74
     75/*
     76 * Include the creation of the trace points after defining the
     77 * wb_writeback_work structure and inline functions so that the definition
     78 * remains local to this file.
     79 */
     80#define CREATE_TRACE_POINTS
     81#include <trace/events/writeback.h>
     82
     83EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
     84
     85static bool wb_io_lists_populated(struct bdi_writeback *wb)
     86{
     87	if (wb_has_dirty_io(wb)) {
     88		return false;
     89	} else {
     90		set_bit(WB_has_dirty_io, &wb->state);
     91		WARN_ON_ONCE(!wb->avg_write_bandwidth);
     92		atomic_long_add(wb->avg_write_bandwidth,
     93				&wb->bdi->tot_write_bandwidth);
     94		return true;
     95	}
     96}
     97
     98static void wb_io_lists_depopulated(struct bdi_writeback *wb)
     99{
    100	if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
    101	    list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
    102		clear_bit(WB_has_dirty_io, &wb->state);
    103		WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
    104					&wb->bdi->tot_write_bandwidth) < 0);
    105	}
    106}
    107
    108/**
    109 * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
    110 * @inode: inode to be moved
    111 * @wb: target bdi_writeback
    112 * @head: one of @wb->b_{dirty|io|more_io|dirty_time}
    113 *
    114 * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
    115 * Returns %true if @inode is the first occupant of the !dirty_time IO
    116 * lists; otherwise, %false.
    117 */
    118static bool inode_io_list_move_locked(struct inode *inode,
    119				      struct bdi_writeback *wb,
    120				      struct list_head *head)
    121{
    122	assert_spin_locked(&wb->list_lock);
    123	assert_spin_locked(&inode->i_lock);
    124
    125	list_move(&inode->i_io_list, head);
    126
    127	/* dirty_time doesn't count as dirty_io until expiration */
    128	if (head != &wb->b_dirty_time)
    129		return wb_io_lists_populated(wb);
    130
    131	wb_io_lists_depopulated(wb);
    132	return false;
    133}
    134
    135static void wb_wakeup(struct bdi_writeback *wb)
    136{
    137	spin_lock_bh(&wb->work_lock);
    138	if (test_bit(WB_registered, &wb->state))
    139		mod_delayed_work(bdi_wq, &wb->dwork, 0);
    140	spin_unlock_bh(&wb->work_lock);
    141}
    142
    143static void finish_writeback_work(struct bdi_writeback *wb,
    144				  struct wb_writeback_work *work)
    145{
    146	struct wb_completion *done = work->done;
    147
    148	if (work->auto_free)
    149		kfree(work);
    150	if (done) {
    151		wait_queue_head_t *waitq = done->waitq;
    152
    153		/* @done can't be accessed after the following dec */
    154		if (atomic_dec_and_test(&done->cnt))
    155			wake_up_all(waitq);
    156	}
    157}
    158
    159static void wb_queue_work(struct bdi_writeback *wb,
    160			  struct wb_writeback_work *work)
    161{
    162	trace_writeback_queue(wb, work);
    163
    164	if (work->done)
    165		atomic_inc(&work->done->cnt);
    166
    167	spin_lock_bh(&wb->work_lock);
    168
    169	if (test_bit(WB_registered, &wb->state)) {
    170		list_add_tail(&work->list, &wb->work_list);
    171		mod_delayed_work(bdi_wq, &wb->dwork, 0);
    172	} else
    173		finish_writeback_work(wb, work);
    174
    175	spin_unlock_bh(&wb->work_lock);
    176}
    177
    178/**
    179 * wb_wait_for_completion - wait for completion of bdi_writeback_works
    180 * @done: target wb_completion
    181 *
    182 * Wait for one or more work items issued to @bdi with their ->done field
    183 * set to @done, which should have been initialized with
    184 * DEFINE_WB_COMPLETION().  This function returns after all such work items
    185 * are completed.  Work items which are waited upon aren't freed
    186 * automatically on completion.
    187 */
    188void wb_wait_for_completion(struct wb_completion *done)
    189{
    190	atomic_dec(&done->cnt);		/* put down the initial count */
    191	wait_event(*done->waitq, !atomic_read(&done->cnt));
    192}
    193
    194#ifdef CONFIG_CGROUP_WRITEBACK
    195
    196/*
    197 * Parameters for foreign inode detection, see wbc_detach_inode() to see
    198 * how they're used.
    199 *
    200 * These paramters are inherently heuristical as the detection target
    201 * itself is fuzzy.  All we want to do is detaching an inode from the
    202 * current owner if it's being written to by some other cgroups too much.
    203 *
    204 * The current cgroup writeback is built on the assumption that multiple
    205 * cgroups writing to the same inode concurrently is very rare and a mode
    206 * of operation which isn't well supported.  As such, the goal is not
    207 * taking too long when a different cgroup takes over an inode while
    208 * avoiding too aggressive flip-flops from occasional foreign writes.
    209 *
    210 * We record, very roughly, 2s worth of IO time history and if more than
    211 * half of that is foreign, trigger the switch.  The recording is quantized
    212 * to 16 slots.  To avoid tiny writes from swinging the decision too much,
    213 * writes smaller than 1/8 of avg size are ignored.
    214 */
    215#define WB_FRN_TIME_SHIFT	13	/* 1s = 2^13, upto 8 secs w/ 16bit */
    216#define WB_FRN_TIME_AVG_SHIFT	3	/* avg = avg * 7/8 + new * 1/8 */
    217#define WB_FRN_TIME_CUT_DIV	8	/* ignore rounds < avg / 8 */
    218#define WB_FRN_TIME_PERIOD	(2 * (1 << WB_FRN_TIME_SHIFT))	/* 2s */
    219
    220#define WB_FRN_HIST_SLOTS	16	/* inode->i_wb_frn_history is 16bit */
    221#define WB_FRN_HIST_UNIT	(WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
    222					/* each slot's duration is 2s / 16 */
    223#define WB_FRN_HIST_THR_SLOTS	(WB_FRN_HIST_SLOTS / 2)
    224					/* if foreign slots >= 8, switch */
    225#define WB_FRN_HIST_MAX_SLOTS	(WB_FRN_HIST_THR_SLOTS / 2 + 1)
    226					/* one round can affect upto 5 slots */
    227#define WB_FRN_MAX_IN_FLIGHT	1024	/* don't queue too many concurrently */
    228
    229/*
    230 * Maximum inodes per isw.  A specific value has been chosen to make
    231 * struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
    232 */
    233#define WB_MAX_INODES_PER_ISW  ((1024UL - sizeof(struct inode_switch_wbs_context)) \
    234                                / sizeof(struct inode *))
    235
    236static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
    237static struct workqueue_struct *isw_wq;
    238
    239void __inode_attach_wb(struct inode *inode, struct page *page)
    240{
    241	struct backing_dev_info *bdi = inode_to_bdi(inode);
    242	struct bdi_writeback *wb = NULL;
    243
    244	if (inode_cgwb_enabled(inode)) {
    245		struct cgroup_subsys_state *memcg_css;
    246
    247		if (page) {
    248			memcg_css = mem_cgroup_css_from_page(page);
    249			wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
    250		} else {
    251			/* must pin memcg_css, see wb_get_create() */
    252			memcg_css = task_get_css(current, memory_cgrp_id);
    253			wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
    254			css_put(memcg_css);
    255		}
    256	}
    257
    258	if (!wb)
    259		wb = &bdi->wb;
    260
    261	/*
    262	 * There may be multiple instances of this function racing to
    263	 * update the same inode.  Use cmpxchg() to tell the winner.
    264	 */
    265	if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
    266		wb_put(wb);
    267}
    268EXPORT_SYMBOL_GPL(__inode_attach_wb);
    269
    270/**
    271 * inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
    272 * @inode: inode of interest with i_lock held
    273 * @wb: target bdi_writeback
    274 *
    275 * Remove the inode from wb's io lists and if necessarily put onto b_attached
    276 * list.  Only inodes attached to cgwb's are kept on this list.
    277 */
    278static void inode_cgwb_move_to_attached(struct inode *inode,
    279					struct bdi_writeback *wb)
    280{
    281	assert_spin_locked(&wb->list_lock);
    282	assert_spin_locked(&inode->i_lock);
    283
    284	inode->i_state &= ~I_SYNC_QUEUED;
    285	if (wb != &wb->bdi->wb)
    286		list_move(&inode->i_io_list, &wb->b_attached);
    287	else
    288		list_del_init(&inode->i_io_list);
    289	wb_io_lists_depopulated(wb);
    290}
    291
    292/**
    293 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
    294 * @inode: inode of interest with i_lock held
    295 *
    296 * Returns @inode's wb with its list_lock held.  @inode->i_lock must be
    297 * held on entry and is released on return.  The returned wb is guaranteed
    298 * to stay @inode's associated wb until its list_lock is released.
    299 */
    300static struct bdi_writeback *
    301locked_inode_to_wb_and_lock_list(struct inode *inode)
    302	__releases(&inode->i_lock)
    303	__acquires(&wb->list_lock)
    304{
    305	while (true) {
    306		struct bdi_writeback *wb = inode_to_wb(inode);
    307
    308		/*
    309		 * inode_to_wb() association is protected by both
    310		 * @inode->i_lock and @wb->list_lock but list_lock nests
    311		 * outside i_lock.  Drop i_lock and verify that the
    312		 * association hasn't changed after acquiring list_lock.
    313		 */
    314		wb_get(wb);
    315		spin_unlock(&inode->i_lock);
    316		spin_lock(&wb->list_lock);
    317
    318		/* i_wb may have changed inbetween, can't use inode_to_wb() */
    319		if (likely(wb == inode->i_wb)) {
    320			wb_put(wb);	/* @inode already has ref */
    321			return wb;
    322		}
    323
    324		spin_unlock(&wb->list_lock);
    325		wb_put(wb);
    326		cpu_relax();
    327		spin_lock(&inode->i_lock);
    328	}
    329}
    330
    331/**
    332 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
    333 * @inode: inode of interest
    334 *
    335 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
    336 * on entry.
    337 */
    338static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
    339	__acquires(&wb->list_lock)
    340{
    341	spin_lock(&inode->i_lock);
    342	return locked_inode_to_wb_and_lock_list(inode);
    343}
    344
    345struct inode_switch_wbs_context {
    346	struct rcu_work		work;
    347
    348	/*
    349	 * Multiple inodes can be switched at once.  The switching procedure
    350	 * consists of two parts, separated by a RCU grace period.  To make
    351	 * sure that the second part is executed for each inode gone through
    352	 * the first part, all inode pointers are placed into a NULL-terminated
    353	 * array embedded into struct inode_switch_wbs_context.  Otherwise
    354	 * an inode could be left in a non-consistent state.
    355	 */
    356	struct bdi_writeback	*new_wb;
    357	struct inode		*inodes[];
    358};
    359
    360static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
    361{
    362	down_write(&bdi->wb_switch_rwsem);
    363}
    364
    365static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
    366{
    367	up_write(&bdi->wb_switch_rwsem);
    368}
    369
    370static bool inode_do_switch_wbs(struct inode *inode,
    371				struct bdi_writeback *old_wb,
    372				struct bdi_writeback *new_wb)
    373{
    374	struct address_space *mapping = inode->i_mapping;
    375	XA_STATE(xas, &mapping->i_pages, 0);
    376	struct folio *folio;
    377	bool switched = false;
    378
    379	spin_lock(&inode->i_lock);
    380	xa_lock_irq(&mapping->i_pages);
    381
    382	/*
    383	 * Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
    384	 * path owns the inode and we shouldn't modify ->i_io_list.
    385	 */
    386	if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
    387		goto skip_switch;
    388
    389	trace_inode_switch_wbs(inode, old_wb, new_wb);
    390
    391	/*
    392	 * Count and transfer stats.  Note that PAGECACHE_TAG_DIRTY points
    393	 * to possibly dirty folios while PAGECACHE_TAG_WRITEBACK points to
    394	 * folios actually under writeback.
    395	 */
    396	xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
    397		if (folio_test_dirty(folio)) {
    398			long nr = folio_nr_pages(folio);
    399			wb_stat_mod(old_wb, WB_RECLAIMABLE, -nr);
    400			wb_stat_mod(new_wb, WB_RECLAIMABLE, nr);
    401		}
    402	}
    403
    404	xas_set(&xas, 0);
    405	xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
    406		long nr = folio_nr_pages(folio);
    407		WARN_ON_ONCE(!folio_test_writeback(folio));
    408		wb_stat_mod(old_wb, WB_WRITEBACK, -nr);
    409		wb_stat_mod(new_wb, WB_WRITEBACK, nr);
    410	}
    411
    412	if (mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) {
    413		atomic_dec(&old_wb->writeback_inodes);
    414		atomic_inc(&new_wb->writeback_inodes);
    415	}
    416
    417	wb_get(new_wb);
    418
    419	/*
    420	 * Transfer to @new_wb's IO list if necessary.  If the @inode is dirty,
    421	 * the specific list @inode was on is ignored and the @inode is put on
    422	 * ->b_dirty which is always correct including from ->b_dirty_time.
    423	 * The transfer preserves @inode->dirtied_when ordering.  If the @inode
    424	 * was clean, it means it was on the b_attached list, so move it onto
    425	 * the b_attached list of @new_wb.
    426	 */
    427	if (!list_empty(&inode->i_io_list)) {
    428		inode->i_wb = new_wb;
    429
    430		if (inode->i_state & I_DIRTY_ALL) {
    431			struct inode *pos;
    432
    433			list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
    434				if (time_after_eq(inode->dirtied_when,
    435						  pos->dirtied_when))
    436					break;
    437			inode_io_list_move_locked(inode, new_wb,
    438						  pos->i_io_list.prev);
    439		} else {
    440			inode_cgwb_move_to_attached(inode, new_wb);
    441		}
    442	} else {
    443		inode->i_wb = new_wb;
    444	}
    445
    446	/* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
    447	inode->i_wb_frn_winner = 0;
    448	inode->i_wb_frn_avg_time = 0;
    449	inode->i_wb_frn_history = 0;
    450	switched = true;
    451skip_switch:
    452	/*
    453	 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
    454	 * ensures that the new wb is visible if they see !I_WB_SWITCH.
    455	 */
    456	smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
    457
    458	xa_unlock_irq(&mapping->i_pages);
    459	spin_unlock(&inode->i_lock);
    460
    461	return switched;
    462}
    463
    464static void inode_switch_wbs_work_fn(struct work_struct *work)
    465{
    466	struct inode_switch_wbs_context *isw =
    467		container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
    468	struct backing_dev_info *bdi = inode_to_bdi(isw->inodes[0]);
    469	struct bdi_writeback *old_wb = isw->inodes[0]->i_wb;
    470	struct bdi_writeback *new_wb = isw->new_wb;
    471	unsigned long nr_switched = 0;
    472	struct inode **inodep;
    473
    474	/*
    475	 * If @inode switches cgwb membership while sync_inodes_sb() is
    476	 * being issued, sync_inodes_sb() might miss it.  Synchronize.
    477	 */
    478	down_read(&bdi->wb_switch_rwsem);
    479
    480	/*
    481	 * By the time control reaches here, RCU grace period has passed
    482	 * since I_WB_SWITCH assertion and all wb stat update transactions
    483	 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
    484	 * synchronizing against the i_pages lock.
    485	 *
    486	 * Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
    487	 * gives us exclusion against all wb related operations on @inode
    488	 * including IO list manipulations and stat updates.
    489	 */
    490	if (old_wb < new_wb) {
    491		spin_lock(&old_wb->list_lock);
    492		spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
    493	} else {
    494		spin_lock(&new_wb->list_lock);
    495		spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
    496	}
    497
    498	for (inodep = isw->inodes; *inodep; inodep++) {
    499		WARN_ON_ONCE((*inodep)->i_wb != old_wb);
    500		if (inode_do_switch_wbs(*inodep, old_wb, new_wb))
    501			nr_switched++;
    502	}
    503
    504	spin_unlock(&new_wb->list_lock);
    505	spin_unlock(&old_wb->list_lock);
    506
    507	up_read(&bdi->wb_switch_rwsem);
    508
    509	if (nr_switched) {
    510		wb_wakeup(new_wb);
    511		wb_put_many(old_wb, nr_switched);
    512	}
    513
    514	for (inodep = isw->inodes; *inodep; inodep++)
    515		iput(*inodep);
    516	wb_put(new_wb);
    517	kfree(isw);
    518	atomic_dec(&isw_nr_in_flight);
    519}
    520
    521static bool inode_prepare_wbs_switch(struct inode *inode,
    522				     struct bdi_writeback *new_wb)
    523{
    524	/*
    525	 * Paired with smp_mb() in cgroup_writeback_umount().
    526	 * isw_nr_in_flight must be increased before checking SB_ACTIVE and
    527	 * grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
    528	 * in cgroup_writeback_umount() and the isw_wq will be not flushed.
    529	 */
    530	smp_mb();
    531
    532	if (IS_DAX(inode))
    533		return false;
    534
    535	/* while holding I_WB_SWITCH, no one else can update the association */
    536	spin_lock(&inode->i_lock);
    537	if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
    538	    inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
    539	    inode_to_wb(inode) == new_wb) {
    540		spin_unlock(&inode->i_lock);
    541		return false;
    542	}
    543	inode->i_state |= I_WB_SWITCH;
    544	__iget(inode);
    545	spin_unlock(&inode->i_lock);
    546
    547	return true;
    548}
    549
    550/**
    551 * inode_switch_wbs - change the wb association of an inode
    552 * @inode: target inode
    553 * @new_wb_id: ID of the new wb
    554 *
    555 * Switch @inode's wb association to the wb identified by @new_wb_id.  The
    556 * switching is performed asynchronously and may fail silently.
    557 */
    558static void inode_switch_wbs(struct inode *inode, int new_wb_id)
    559{
    560	struct backing_dev_info *bdi = inode_to_bdi(inode);
    561	struct cgroup_subsys_state *memcg_css;
    562	struct inode_switch_wbs_context *isw;
    563
    564	/* noop if seems to be already in progress */
    565	if (inode->i_state & I_WB_SWITCH)
    566		return;
    567
    568	/* avoid queueing a new switch if too many are already in flight */
    569	if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
    570		return;
    571
    572	isw = kzalloc(struct_size(isw, inodes, 2), GFP_ATOMIC);
    573	if (!isw)
    574		return;
    575
    576	atomic_inc(&isw_nr_in_flight);
    577
    578	/* find and pin the new wb */
    579	rcu_read_lock();
    580	memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
    581	if (memcg_css && !css_tryget(memcg_css))
    582		memcg_css = NULL;
    583	rcu_read_unlock();
    584	if (!memcg_css)
    585		goto out_free;
    586
    587	isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
    588	css_put(memcg_css);
    589	if (!isw->new_wb)
    590		goto out_free;
    591
    592	if (!inode_prepare_wbs_switch(inode, isw->new_wb))
    593		goto out_free;
    594
    595	isw->inodes[0] = inode;
    596
    597	/*
    598	 * In addition to synchronizing among switchers, I_WB_SWITCH tells
    599	 * the RCU protected stat update paths to grab the i_page
    600	 * lock so that stat transfer can synchronize against them.
    601	 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
    602	 */
    603	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
    604	queue_rcu_work(isw_wq, &isw->work);
    605	return;
    606
    607out_free:
    608	atomic_dec(&isw_nr_in_flight);
    609	if (isw->new_wb)
    610		wb_put(isw->new_wb);
    611	kfree(isw);
    612}
    613
    614/**
    615 * cleanup_offline_cgwb - detach associated inodes
    616 * @wb: target wb
    617 *
    618 * Switch all inodes attached to @wb to a nearest living ancestor's wb in order
    619 * to eventually release the dying @wb.  Returns %true if not all inodes were
    620 * switched and the function has to be restarted.
    621 */
    622bool cleanup_offline_cgwb(struct bdi_writeback *wb)
    623{
    624	struct cgroup_subsys_state *memcg_css;
    625	struct inode_switch_wbs_context *isw;
    626	struct inode *inode;
    627	int nr;
    628	bool restart = false;
    629
    630	isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW),
    631		      GFP_KERNEL);
    632	if (!isw)
    633		return restart;
    634
    635	atomic_inc(&isw_nr_in_flight);
    636
    637	for (memcg_css = wb->memcg_css->parent; memcg_css;
    638	     memcg_css = memcg_css->parent) {
    639		isw->new_wb = wb_get_create(wb->bdi, memcg_css, GFP_KERNEL);
    640		if (isw->new_wb)
    641			break;
    642	}
    643	if (unlikely(!isw->new_wb))
    644		isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
    645
    646	nr = 0;
    647	spin_lock(&wb->list_lock);
    648	list_for_each_entry(inode, &wb->b_attached, i_io_list) {
    649		if (!inode_prepare_wbs_switch(inode, isw->new_wb))
    650			continue;
    651
    652		isw->inodes[nr++] = inode;
    653
    654		if (nr >= WB_MAX_INODES_PER_ISW - 1) {
    655			restart = true;
    656			break;
    657		}
    658	}
    659	spin_unlock(&wb->list_lock);
    660
    661	/* no attached inodes? bail out */
    662	if (nr == 0) {
    663		atomic_dec(&isw_nr_in_flight);
    664		wb_put(isw->new_wb);
    665		kfree(isw);
    666		return restart;
    667	}
    668
    669	/*
    670	 * In addition to synchronizing among switchers, I_WB_SWITCH tells
    671	 * the RCU protected stat update paths to grab the i_page
    672	 * lock so that stat transfer can synchronize against them.
    673	 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
    674	 */
    675	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
    676	queue_rcu_work(isw_wq, &isw->work);
    677
    678	return restart;
    679}
    680
    681/**
    682 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
    683 * @wbc: writeback_control of interest
    684 * @inode: target inode
    685 *
    686 * @inode is locked and about to be written back under the control of @wbc.
    687 * Record @inode's writeback context into @wbc and unlock the i_lock.  On
    688 * writeback completion, wbc_detach_inode() should be called.  This is used
    689 * to track the cgroup writeback context.
    690 */
    691void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
    692				 struct inode *inode)
    693{
    694	if (!inode_cgwb_enabled(inode)) {
    695		spin_unlock(&inode->i_lock);
    696		return;
    697	}
    698
    699	wbc->wb = inode_to_wb(inode);
    700	wbc->inode = inode;
    701
    702	wbc->wb_id = wbc->wb->memcg_css->id;
    703	wbc->wb_lcand_id = inode->i_wb_frn_winner;
    704	wbc->wb_tcand_id = 0;
    705	wbc->wb_bytes = 0;
    706	wbc->wb_lcand_bytes = 0;
    707	wbc->wb_tcand_bytes = 0;
    708
    709	wb_get(wbc->wb);
    710	spin_unlock(&inode->i_lock);
    711
    712	/*
    713	 * A dying wb indicates that either the blkcg associated with the
    714	 * memcg changed or the associated memcg is dying.  In the first
    715	 * case, a replacement wb should already be available and we should
    716	 * refresh the wb immediately.  In the second case, trying to
    717	 * refresh will keep failing.
    718	 */
    719	if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
    720		inode_switch_wbs(inode, wbc->wb_id);
    721}
    722EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
    723
    724/**
    725 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
    726 * @wbc: writeback_control of the just finished writeback
    727 *
    728 * To be called after a writeback attempt of an inode finishes and undoes
    729 * wbc_attach_and_unlock_inode().  Can be called under any context.
    730 *
    731 * As concurrent write sharing of an inode is expected to be very rare and
    732 * memcg only tracks page ownership on first-use basis severely confining
    733 * the usefulness of such sharing, cgroup writeback tracks ownership
    734 * per-inode.  While the support for concurrent write sharing of an inode
    735 * is deemed unnecessary, an inode being written to by different cgroups at
    736 * different points in time is a lot more common, and, more importantly,
    737 * charging only by first-use can too readily lead to grossly incorrect
    738 * behaviors (single foreign page can lead to gigabytes of writeback to be
    739 * incorrectly attributed).
    740 *
    741 * To resolve this issue, cgroup writeback detects the majority dirtier of
    742 * an inode and transfers the ownership to it.  To avoid unnecessary
    743 * oscillation, the detection mechanism keeps track of history and gives
    744 * out the switch verdict only if the foreign usage pattern is stable over
    745 * a certain amount of time and/or writeback attempts.
    746 *
    747 * On each writeback attempt, @wbc tries to detect the majority writer
    748 * using Boyer-Moore majority vote algorithm.  In addition to the byte
    749 * count from the majority voting, it also counts the bytes written for the
    750 * current wb and the last round's winner wb (max of last round's current
    751 * wb, the winner from two rounds ago, and the last round's majority
    752 * candidate).  Keeping track of the historical winner helps the algorithm
    753 * to semi-reliably detect the most active writer even when it's not the
    754 * absolute majority.
    755 *
    756 * Once the winner of the round is determined, whether the winner is
    757 * foreign or not and how much IO time the round consumed is recorded in
    758 * inode->i_wb_frn_history.  If the amount of recorded foreign IO time is
    759 * over a certain threshold, the switch verdict is given.
    760 */
    761void wbc_detach_inode(struct writeback_control *wbc)
    762{
    763	struct bdi_writeback *wb = wbc->wb;
    764	struct inode *inode = wbc->inode;
    765	unsigned long avg_time, max_bytes, max_time;
    766	u16 history;
    767	int max_id;
    768
    769	if (!wb)
    770		return;
    771
    772	history = inode->i_wb_frn_history;
    773	avg_time = inode->i_wb_frn_avg_time;
    774
    775	/* pick the winner of this round */
    776	if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
    777	    wbc->wb_bytes >= wbc->wb_tcand_bytes) {
    778		max_id = wbc->wb_id;
    779		max_bytes = wbc->wb_bytes;
    780	} else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
    781		max_id = wbc->wb_lcand_id;
    782		max_bytes = wbc->wb_lcand_bytes;
    783	} else {
    784		max_id = wbc->wb_tcand_id;
    785		max_bytes = wbc->wb_tcand_bytes;
    786	}
    787
    788	/*
    789	 * Calculate the amount of IO time the winner consumed and fold it
    790	 * into the running average kept per inode.  If the consumed IO
    791	 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
    792	 * deciding whether to switch or not.  This is to prevent one-off
    793	 * small dirtiers from skewing the verdict.
    794	 */
    795	max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
    796				wb->avg_write_bandwidth);
    797	if (avg_time)
    798		avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
    799			    (avg_time >> WB_FRN_TIME_AVG_SHIFT);
    800	else
    801		avg_time = max_time;	/* immediate catch up on first run */
    802
    803	if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
    804		int slots;
    805
    806		/*
    807		 * The switch verdict is reached if foreign wb's consume
    808		 * more than a certain proportion of IO time in a
    809		 * WB_FRN_TIME_PERIOD.  This is loosely tracked by 16 slot
    810		 * history mask where each bit represents one sixteenth of
    811		 * the period.  Determine the number of slots to shift into
    812		 * history from @max_time.
    813		 */
    814		slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
    815			    (unsigned long)WB_FRN_HIST_MAX_SLOTS);
    816		history <<= slots;
    817		if (wbc->wb_id != max_id)
    818			history |= (1U << slots) - 1;
    819
    820		if (history)
    821			trace_inode_foreign_history(inode, wbc, history);
    822
    823		/*
    824		 * Switch if the current wb isn't the consistent winner.
    825		 * If there are multiple closely competing dirtiers, the
    826		 * inode may switch across them repeatedly over time, which
    827		 * is okay.  The main goal is avoiding keeping an inode on
    828		 * the wrong wb for an extended period of time.
    829		 */
    830		if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
    831			inode_switch_wbs(inode, max_id);
    832	}
    833
    834	/*
    835	 * Multiple instances of this function may race to update the
    836	 * following fields but we don't mind occassional inaccuracies.
    837	 */
    838	inode->i_wb_frn_winner = max_id;
    839	inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
    840	inode->i_wb_frn_history = history;
    841
    842	wb_put(wbc->wb);
    843	wbc->wb = NULL;
    844}
    845EXPORT_SYMBOL_GPL(wbc_detach_inode);
    846
    847/**
    848 * wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
    849 * @wbc: writeback_control of the writeback in progress
    850 * @page: page being written out
    851 * @bytes: number of bytes being written out
    852 *
    853 * @bytes from @page are about to written out during the writeback
    854 * controlled by @wbc.  Keep the book for foreign inode detection.  See
    855 * wbc_detach_inode().
    856 */
    857void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
    858			      size_t bytes)
    859{
    860	struct cgroup_subsys_state *css;
    861	int id;
    862
    863	/*
    864	 * pageout() path doesn't attach @wbc to the inode being written
    865	 * out.  This is intentional as we don't want the function to block
    866	 * behind a slow cgroup.  Ultimately, we want pageout() to kick off
    867	 * regular writeback instead of writing things out itself.
    868	 */
    869	if (!wbc->wb || wbc->no_cgroup_owner)
    870		return;
    871
    872	css = mem_cgroup_css_from_page(page);
    873	/* dead cgroups shouldn't contribute to inode ownership arbitration */
    874	if (!(css->flags & CSS_ONLINE))
    875		return;
    876
    877	id = css->id;
    878
    879	if (id == wbc->wb_id) {
    880		wbc->wb_bytes += bytes;
    881		return;
    882	}
    883
    884	if (id == wbc->wb_lcand_id)
    885		wbc->wb_lcand_bytes += bytes;
    886
    887	/* Boyer-Moore majority vote algorithm */
    888	if (!wbc->wb_tcand_bytes)
    889		wbc->wb_tcand_id = id;
    890	if (id == wbc->wb_tcand_id)
    891		wbc->wb_tcand_bytes += bytes;
    892	else
    893		wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
    894}
    895EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
    896
    897/**
    898 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
    899 * @wb: target bdi_writeback to split @nr_pages to
    900 * @nr_pages: number of pages to write for the whole bdi
    901 *
    902 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
    903 * relation to the total write bandwidth of all wb's w/ dirty inodes on
    904 * @wb->bdi.
    905 */
    906static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
    907{
    908	unsigned long this_bw = wb->avg_write_bandwidth;
    909	unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
    910
    911	if (nr_pages == LONG_MAX)
    912		return LONG_MAX;
    913
    914	/*
    915	 * This may be called on clean wb's and proportional distribution
    916	 * may not make sense, just use the original @nr_pages in those
    917	 * cases.  In general, we wanna err on the side of writing more.
    918	 */
    919	if (!tot_bw || this_bw >= tot_bw)
    920		return nr_pages;
    921	else
    922		return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
    923}
    924
    925/**
    926 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
    927 * @bdi: target backing_dev_info
    928 * @base_work: wb_writeback_work to issue
    929 * @skip_if_busy: skip wb's which already have writeback in progress
    930 *
    931 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
    932 * have dirty inodes.  If @base_work->nr_page isn't %LONG_MAX, it's
    933 * distributed to the busy wbs according to each wb's proportion in the
    934 * total active write bandwidth of @bdi.
    935 */
    936static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
    937				  struct wb_writeback_work *base_work,
    938				  bool skip_if_busy)
    939{
    940	struct bdi_writeback *last_wb = NULL;
    941	struct bdi_writeback *wb = list_entry(&bdi->wb_list,
    942					      struct bdi_writeback, bdi_node);
    943
    944	might_sleep();
    945restart:
    946	rcu_read_lock();
    947	list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
    948		DEFINE_WB_COMPLETION(fallback_work_done, bdi);
    949		struct wb_writeback_work fallback_work;
    950		struct wb_writeback_work *work;
    951		long nr_pages;
    952
    953		if (last_wb) {
    954			wb_put(last_wb);
    955			last_wb = NULL;
    956		}
    957
    958		/* SYNC_ALL writes out I_DIRTY_TIME too */
    959		if (!wb_has_dirty_io(wb) &&
    960		    (base_work->sync_mode == WB_SYNC_NONE ||
    961		     list_empty(&wb->b_dirty_time)))
    962			continue;
    963		if (skip_if_busy && writeback_in_progress(wb))
    964			continue;
    965
    966		nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
    967
    968		work = kmalloc(sizeof(*work), GFP_ATOMIC);
    969		if (work) {
    970			*work = *base_work;
    971			work->nr_pages = nr_pages;
    972			work->auto_free = 1;
    973			wb_queue_work(wb, work);
    974			continue;
    975		}
    976
    977		/* alloc failed, execute synchronously using on-stack fallback */
    978		work = &fallback_work;
    979		*work = *base_work;
    980		work->nr_pages = nr_pages;
    981		work->auto_free = 0;
    982		work->done = &fallback_work_done;
    983
    984		wb_queue_work(wb, work);
    985
    986		/*
    987		 * Pin @wb so that it stays on @bdi->wb_list.  This allows
    988		 * continuing iteration from @wb after dropping and
    989		 * regrabbing rcu read lock.
    990		 */
    991		wb_get(wb);
    992		last_wb = wb;
    993
    994		rcu_read_unlock();
    995		wb_wait_for_completion(&fallback_work_done);
    996		goto restart;
    997	}
    998	rcu_read_unlock();
    999
   1000	if (last_wb)
   1001		wb_put(last_wb);
   1002}
   1003
   1004/**
   1005 * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
   1006 * @bdi_id: target bdi id
   1007 * @memcg_id: target memcg css id
   1008 * @reason: reason why some writeback work initiated
   1009 * @done: target wb_completion
   1010 *
   1011 * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
   1012 * with the specified parameters.
   1013 */
   1014int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
   1015			   enum wb_reason reason, struct wb_completion *done)
   1016{
   1017	struct backing_dev_info *bdi;
   1018	struct cgroup_subsys_state *memcg_css;
   1019	struct bdi_writeback *wb;
   1020	struct wb_writeback_work *work;
   1021	unsigned long dirty;
   1022	int ret;
   1023
   1024	/* lookup bdi and memcg */
   1025	bdi = bdi_get_by_id(bdi_id);
   1026	if (!bdi)
   1027		return -ENOENT;
   1028
   1029	rcu_read_lock();
   1030	memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
   1031	if (memcg_css && !css_tryget(memcg_css))
   1032		memcg_css = NULL;
   1033	rcu_read_unlock();
   1034	if (!memcg_css) {
   1035		ret = -ENOENT;
   1036		goto out_bdi_put;
   1037	}
   1038
   1039	/*
   1040	 * And find the associated wb.  If the wb isn't there already
   1041	 * there's nothing to flush, don't create one.
   1042	 */
   1043	wb = wb_get_lookup(bdi, memcg_css);
   1044	if (!wb) {
   1045		ret = -ENOENT;
   1046		goto out_css_put;
   1047	}
   1048
   1049	/*
   1050	 * The caller is attempting to write out most of
   1051	 * the currently dirty pages.  Let's take the current dirty page
   1052	 * count and inflate it by 25% which should be large enough to
   1053	 * flush out most dirty pages while avoiding getting livelocked by
   1054	 * concurrent dirtiers.
   1055	 *
   1056	 * BTW the memcg stats are flushed periodically and this is best-effort
   1057	 * estimation, so some potential error is ok.
   1058	 */
   1059	dirty = memcg_page_state(mem_cgroup_from_css(memcg_css), NR_FILE_DIRTY);
   1060	dirty = dirty * 10 / 8;
   1061
   1062	/* issue the writeback work */
   1063	work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
   1064	if (work) {
   1065		work->nr_pages = dirty;
   1066		work->sync_mode = WB_SYNC_NONE;
   1067		work->range_cyclic = 1;
   1068		work->reason = reason;
   1069		work->done = done;
   1070		work->auto_free = 1;
   1071		wb_queue_work(wb, work);
   1072		ret = 0;
   1073	} else {
   1074		ret = -ENOMEM;
   1075	}
   1076
   1077	wb_put(wb);
   1078out_css_put:
   1079	css_put(memcg_css);
   1080out_bdi_put:
   1081	bdi_put(bdi);
   1082	return ret;
   1083}
   1084
   1085/**
   1086 * cgroup_writeback_umount - flush inode wb switches for umount
   1087 *
   1088 * This function is called when a super_block is about to be destroyed and
   1089 * flushes in-flight inode wb switches.  An inode wb switch goes through
   1090 * RCU and then workqueue, so the two need to be flushed in order to ensure
   1091 * that all previously scheduled switches are finished.  As wb switches are
   1092 * rare occurrences and synchronize_rcu() can take a while, perform
   1093 * flushing iff wb switches are in flight.
   1094 */
   1095void cgroup_writeback_umount(void)
   1096{
   1097	/*
   1098	 * SB_ACTIVE should be reliably cleared before checking
   1099	 * isw_nr_in_flight, see generic_shutdown_super().
   1100	 */
   1101	smp_mb();
   1102
   1103	if (atomic_read(&isw_nr_in_flight)) {
   1104		/*
   1105		 * Use rcu_barrier() to wait for all pending callbacks to
   1106		 * ensure that all in-flight wb switches are in the workqueue.
   1107		 */
   1108		rcu_barrier();
   1109		flush_workqueue(isw_wq);
   1110	}
   1111}
   1112
   1113static int __init cgroup_writeback_init(void)
   1114{
   1115	isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
   1116	if (!isw_wq)
   1117		return -ENOMEM;
   1118	return 0;
   1119}
   1120fs_initcall(cgroup_writeback_init);
   1121
   1122#else	/* CONFIG_CGROUP_WRITEBACK */
   1123
   1124static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
   1125static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
   1126
   1127static void inode_cgwb_move_to_attached(struct inode *inode,
   1128					struct bdi_writeback *wb)
   1129{
   1130	assert_spin_locked(&wb->list_lock);
   1131	assert_spin_locked(&inode->i_lock);
   1132
   1133	inode->i_state &= ~I_SYNC_QUEUED;
   1134	list_del_init(&inode->i_io_list);
   1135	wb_io_lists_depopulated(wb);
   1136}
   1137
   1138static struct bdi_writeback *
   1139locked_inode_to_wb_and_lock_list(struct inode *inode)
   1140	__releases(&inode->i_lock)
   1141	__acquires(&wb->list_lock)
   1142{
   1143	struct bdi_writeback *wb = inode_to_wb(inode);
   1144
   1145	spin_unlock(&inode->i_lock);
   1146	spin_lock(&wb->list_lock);
   1147	return wb;
   1148}
   1149
   1150static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
   1151	__acquires(&wb->list_lock)
   1152{
   1153	struct bdi_writeback *wb = inode_to_wb(inode);
   1154
   1155	spin_lock(&wb->list_lock);
   1156	return wb;
   1157}
   1158
   1159static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
   1160{
   1161	return nr_pages;
   1162}
   1163
   1164static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
   1165				  struct wb_writeback_work *base_work,
   1166				  bool skip_if_busy)
   1167{
   1168	might_sleep();
   1169
   1170	if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
   1171		base_work->auto_free = 0;
   1172		wb_queue_work(&bdi->wb, base_work);
   1173	}
   1174}
   1175
   1176#endif	/* CONFIG_CGROUP_WRITEBACK */
   1177
   1178/*
   1179 * Add in the number of potentially dirty inodes, because each inode
   1180 * write can dirty pagecache in the underlying blockdev.
   1181 */
   1182static unsigned long get_nr_dirty_pages(void)
   1183{
   1184	return global_node_page_state(NR_FILE_DIRTY) +
   1185		get_nr_dirty_inodes();
   1186}
   1187
   1188static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
   1189{
   1190	if (!wb_has_dirty_io(wb))
   1191		return;
   1192
   1193	/*
   1194	 * All callers of this function want to start writeback of all
   1195	 * dirty pages. Places like vmscan can call this at a very
   1196	 * high frequency, causing pointless allocations of tons of
   1197	 * work items and keeping the flusher threads busy retrieving
   1198	 * that work. Ensure that we only allow one of them pending and
   1199	 * inflight at the time.
   1200	 */
   1201	if (test_bit(WB_start_all, &wb->state) ||
   1202	    test_and_set_bit(WB_start_all, &wb->state))
   1203		return;
   1204
   1205	wb->start_all_reason = reason;
   1206	wb_wakeup(wb);
   1207}
   1208
   1209/**
   1210 * wb_start_background_writeback - start background writeback
   1211 * @wb: bdi_writback to write from
   1212 *
   1213 * Description:
   1214 *   This makes sure WB_SYNC_NONE background writeback happens. When
   1215 *   this function returns, it is only guaranteed that for given wb
   1216 *   some IO is happening if we are over background dirty threshold.
   1217 *   Caller need not hold sb s_umount semaphore.
   1218 */
   1219void wb_start_background_writeback(struct bdi_writeback *wb)
   1220{
   1221	/*
   1222	 * We just wake up the flusher thread. It will perform background
   1223	 * writeback as soon as there is no other work to do.
   1224	 */
   1225	trace_writeback_wake_background(wb);
   1226	wb_wakeup(wb);
   1227}
   1228
   1229/*
   1230 * Remove the inode from the writeback list it is on.
   1231 */
   1232void inode_io_list_del(struct inode *inode)
   1233{
   1234	struct bdi_writeback *wb;
   1235
   1236	wb = inode_to_wb_and_lock_list(inode);
   1237	spin_lock(&inode->i_lock);
   1238
   1239	inode->i_state &= ~I_SYNC_QUEUED;
   1240	list_del_init(&inode->i_io_list);
   1241	wb_io_lists_depopulated(wb);
   1242
   1243	spin_unlock(&inode->i_lock);
   1244	spin_unlock(&wb->list_lock);
   1245}
   1246EXPORT_SYMBOL(inode_io_list_del);
   1247
   1248/*
   1249 * mark an inode as under writeback on the sb
   1250 */
   1251void sb_mark_inode_writeback(struct inode *inode)
   1252{
   1253	struct super_block *sb = inode->i_sb;
   1254	unsigned long flags;
   1255
   1256	if (list_empty(&inode->i_wb_list)) {
   1257		spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
   1258		if (list_empty(&inode->i_wb_list)) {
   1259			list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
   1260			trace_sb_mark_inode_writeback(inode);
   1261		}
   1262		spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
   1263	}
   1264}
   1265
   1266/*
   1267 * clear an inode as under writeback on the sb
   1268 */
   1269void sb_clear_inode_writeback(struct inode *inode)
   1270{
   1271	struct super_block *sb = inode->i_sb;
   1272	unsigned long flags;
   1273
   1274	if (!list_empty(&inode->i_wb_list)) {
   1275		spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
   1276		if (!list_empty(&inode->i_wb_list)) {
   1277			list_del_init(&inode->i_wb_list);
   1278			trace_sb_clear_inode_writeback(inode);
   1279		}
   1280		spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
   1281	}
   1282}
   1283
   1284/*
   1285 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
   1286 * furthest end of its superblock's dirty-inode list.
   1287 *
   1288 * Before stamping the inode's ->dirtied_when, we check to see whether it is
   1289 * already the most-recently-dirtied inode on the b_dirty list.  If that is
   1290 * the case then the inode must have been redirtied while it was being written
   1291 * out and we don't reset its dirtied_when.
   1292 */
   1293static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
   1294{
   1295	assert_spin_locked(&inode->i_lock);
   1296
   1297	if (!list_empty(&wb->b_dirty)) {
   1298		struct inode *tail;
   1299
   1300		tail = wb_inode(wb->b_dirty.next);
   1301		if (time_before(inode->dirtied_when, tail->dirtied_when))
   1302			inode->dirtied_when = jiffies;
   1303	}
   1304	inode_io_list_move_locked(inode, wb, &wb->b_dirty);
   1305	inode->i_state &= ~I_SYNC_QUEUED;
   1306}
   1307
   1308static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
   1309{
   1310	spin_lock(&inode->i_lock);
   1311	redirty_tail_locked(inode, wb);
   1312	spin_unlock(&inode->i_lock);
   1313}
   1314
   1315/*
   1316 * requeue inode for re-scanning after bdi->b_io list is exhausted.
   1317 */
   1318static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
   1319{
   1320	inode_io_list_move_locked(inode, wb, &wb->b_more_io);
   1321}
   1322
   1323static void inode_sync_complete(struct inode *inode)
   1324{
   1325	inode->i_state &= ~I_SYNC;
   1326	/* If inode is clean an unused, put it into LRU now... */
   1327	inode_add_lru(inode);
   1328	/* Waiters must see I_SYNC cleared before being woken up */
   1329	smp_mb();
   1330	wake_up_bit(&inode->i_state, __I_SYNC);
   1331}
   1332
   1333static bool inode_dirtied_after(struct inode *inode, unsigned long t)
   1334{
   1335	bool ret = time_after(inode->dirtied_when, t);
   1336#ifndef CONFIG_64BIT
   1337	/*
   1338	 * For inodes being constantly redirtied, dirtied_when can get stuck.
   1339	 * It _appears_ to be in the future, but is actually in distant past.
   1340	 * This test is necessary to prevent such wrapped-around relative times
   1341	 * from permanently stopping the whole bdi writeback.
   1342	 */
   1343	ret = ret && time_before_eq(inode->dirtied_when, jiffies);
   1344#endif
   1345	return ret;
   1346}
   1347
   1348#define EXPIRE_DIRTY_ATIME 0x0001
   1349
   1350/*
   1351 * Move expired (dirtied before dirtied_before) dirty inodes from
   1352 * @delaying_queue to @dispatch_queue.
   1353 */
   1354static int move_expired_inodes(struct list_head *delaying_queue,
   1355			       struct list_head *dispatch_queue,
   1356			       unsigned long dirtied_before)
   1357{
   1358	LIST_HEAD(tmp);
   1359	struct list_head *pos, *node;
   1360	struct super_block *sb = NULL;
   1361	struct inode *inode;
   1362	int do_sb_sort = 0;
   1363	int moved = 0;
   1364
   1365	while (!list_empty(delaying_queue)) {
   1366		inode = wb_inode(delaying_queue->prev);
   1367		if (inode_dirtied_after(inode, dirtied_before))
   1368			break;
   1369		spin_lock(&inode->i_lock);
   1370		list_move(&inode->i_io_list, &tmp);
   1371		moved++;
   1372		inode->i_state |= I_SYNC_QUEUED;
   1373		spin_unlock(&inode->i_lock);
   1374		if (sb_is_blkdev_sb(inode->i_sb))
   1375			continue;
   1376		if (sb && sb != inode->i_sb)
   1377			do_sb_sort = 1;
   1378		sb = inode->i_sb;
   1379	}
   1380
   1381	/* just one sb in list, splice to dispatch_queue and we're done */
   1382	if (!do_sb_sort) {
   1383		list_splice(&tmp, dispatch_queue);
   1384		goto out;
   1385	}
   1386
   1387	/*
   1388	 * Although inode's i_io_list is moved from 'tmp' to 'dispatch_queue',
   1389	 * we don't take inode->i_lock here because it is just a pointless overhead.
   1390	 * Inode is already marked as I_SYNC_QUEUED so writeback list handling is
   1391	 * fully under our control.
   1392	 */
   1393	while (!list_empty(&tmp)) {
   1394		sb = wb_inode(tmp.prev)->i_sb;
   1395		list_for_each_prev_safe(pos, node, &tmp) {
   1396			inode = wb_inode(pos);
   1397			if (inode->i_sb == sb)
   1398				list_move(&inode->i_io_list, dispatch_queue);
   1399		}
   1400	}
   1401out:
   1402	return moved;
   1403}
   1404
   1405/*
   1406 * Queue all expired dirty inodes for io, eldest first.
   1407 * Before
   1408 *         newly dirtied     b_dirty    b_io    b_more_io
   1409 *         =============>    gf         edc     BA
   1410 * After
   1411 *         newly dirtied     b_dirty    b_io    b_more_io
   1412 *         =============>    g          fBAedc
   1413 *                                           |
   1414 *                                           +--> dequeue for IO
   1415 */
   1416static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
   1417		     unsigned long dirtied_before)
   1418{
   1419	int moved;
   1420	unsigned long time_expire_jif = dirtied_before;
   1421
   1422	assert_spin_locked(&wb->list_lock);
   1423	list_splice_init(&wb->b_more_io, &wb->b_io);
   1424	moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, dirtied_before);
   1425	if (!work->for_sync)
   1426		time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
   1427	moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
   1428				     time_expire_jif);
   1429	if (moved)
   1430		wb_io_lists_populated(wb);
   1431	trace_writeback_queue_io(wb, work, dirtied_before, moved);
   1432}
   1433
   1434static int write_inode(struct inode *inode, struct writeback_control *wbc)
   1435{
   1436	int ret;
   1437
   1438	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
   1439		trace_writeback_write_inode_start(inode, wbc);
   1440		ret = inode->i_sb->s_op->write_inode(inode, wbc);
   1441		trace_writeback_write_inode(inode, wbc);
   1442		return ret;
   1443	}
   1444	return 0;
   1445}
   1446
   1447/*
   1448 * Wait for writeback on an inode to complete. Called with i_lock held.
   1449 * Caller must make sure inode cannot go away when we drop i_lock.
   1450 */
   1451static void __inode_wait_for_writeback(struct inode *inode)
   1452	__releases(inode->i_lock)
   1453	__acquires(inode->i_lock)
   1454{
   1455	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
   1456	wait_queue_head_t *wqh;
   1457
   1458	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
   1459	while (inode->i_state & I_SYNC) {
   1460		spin_unlock(&inode->i_lock);
   1461		__wait_on_bit(wqh, &wq, bit_wait,
   1462			      TASK_UNINTERRUPTIBLE);
   1463		spin_lock(&inode->i_lock);
   1464	}
   1465}
   1466
   1467/*
   1468 * Wait for writeback on an inode to complete. Caller must have inode pinned.
   1469 */
   1470void inode_wait_for_writeback(struct inode *inode)
   1471{
   1472	spin_lock(&inode->i_lock);
   1473	__inode_wait_for_writeback(inode);
   1474	spin_unlock(&inode->i_lock);
   1475}
   1476
   1477/*
   1478 * Sleep until I_SYNC is cleared. This function must be called with i_lock
   1479 * held and drops it. It is aimed for callers not holding any inode reference
   1480 * so once i_lock is dropped, inode can go away.
   1481 */
   1482static void inode_sleep_on_writeback(struct inode *inode)
   1483	__releases(inode->i_lock)
   1484{
   1485	DEFINE_WAIT(wait);
   1486	wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
   1487	int sleep;
   1488
   1489	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
   1490	sleep = inode->i_state & I_SYNC;
   1491	spin_unlock(&inode->i_lock);
   1492	if (sleep)
   1493		schedule();
   1494	finish_wait(wqh, &wait);
   1495}
   1496
   1497/*
   1498 * Find proper writeback list for the inode depending on its current state and
   1499 * possibly also change of its state while we were doing writeback.  Here we
   1500 * handle things such as livelock prevention or fairness of writeback among
   1501 * inodes. This function can be called only by flusher thread - noone else
   1502 * processes all inodes in writeback lists and requeueing inodes behind flusher
   1503 * thread's back can have unexpected consequences.
   1504 */
   1505static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
   1506			  struct writeback_control *wbc)
   1507{
   1508	if (inode->i_state & I_FREEING)
   1509		return;
   1510
   1511	/*
   1512	 * Sync livelock prevention. Each inode is tagged and synced in one
   1513	 * shot. If still dirty, it will be redirty_tail()'ed below.  Update
   1514	 * the dirty time to prevent enqueue and sync it again.
   1515	 */
   1516	if ((inode->i_state & I_DIRTY) &&
   1517	    (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
   1518		inode->dirtied_when = jiffies;
   1519
   1520	if (wbc->pages_skipped) {
   1521		/*
   1522		 * writeback is not making progress due to locked
   1523		 * buffers. Skip this inode for now.
   1524		 */
   1525		redirty_tail_locked(inode, wb);
   1526		return;
   1527	}
   1528
   1529	if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
   1530		/*
   1531		 * We didn't write back all the pages.  nfs_writepages()
   1532		 * sometimes bales out without doing anything.
   1533		 */
   1534		if (wbc->nr_to_write <= 0) {
   1535			/* Slice used up. Queue for next turn. */
   1536			requeue_io(inode, wb);
   1537		} else {
   1538			/*
   1539			 * Writeback blocked by something other than
   1540			 * congestion. Delay the inode for some time to
   1541			 * avoid spinning on the CPU (100% iowait)
   1542			 * retrying writeback of the dirty page/inode
   1543			 * that cannot be performed immediately.
   1544			 */
   1545			redirty_tail_locked(inode, wb);
   1546		}
   1547	} else if (inode->i_state & I_DIRTY) {
   1548		/*
   1549		 * Filesystems can dirty the inode during writeback operations,
   1550		 * such as delayed allocation during submission or metadata
   1551		 * updates after data IO completion.
   1552		 */
   1553		redirty_tail_locked(inode, wb);
   1554	} else if (inode->i_state & I_DIRTY_TIME) {
   1555		inode->dirtied_when = jiffies;
   1556		inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
   1557		inode->i_state &= ~I_SYNC_QUEUED;
   1558	} else {
   1559		/* The inode is clean. Remove from writeback lists. */
   1560		inode_cgwb_move_to_attached(inode, wb);
   1561	}
   1562}
   1563
   1564/*
   1565 * Write out an inode and its dirty pages (or some of its dirty pages, depending
   1566 * on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
   1567 *
   1568 * This doesn't remove the inode from the writeback list it is on, except
   1569 * potentially to move it from b_dirty_time to b_dirty due to timestamp
   1570 * expiration.  The caller is otherwise responsible for writeback list handling.
   1571 *
   1572 * The caller is also responsible for setting the I_SYNC flag beforehand and
   1573 * calling inode_sync_complete() to clear it afterwards.
   1574 */
   1575static int
   1576__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
   1577{
   1578	struct address_space *mapping = inode->i_mapping;
   1579	long nr_to_write = wbc->nr_to_write;
   1580	unsigned dirty;
   1581	int ret;
   1582
   1583	WARN_ON(!(inode->i_state & I_SYNC));
   1584
   1585	trace_writeback_single_inode_start(inode, wbc, nr_to_write);
   1586
   1587	ret = do_writepages(mapping, wbc);
   1588
   1589	/*
   1590	 * Make sure to wait on the data before writing out the metadata.
   1591	 * This is important for filesystems that modify metadata on data
   1592	 * I/O completion. We don't do it for sync(2) writeback because it has a
   1593	 * separate, external IO completion path and ->sync_fs for guaranteeing
   1594	 * inode metadata is written back correctly.
   1595	 */
   1596	if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
   1597		int err = filemap_fdatawait(mapping);
   1598		if (ret == 0)
   1599			ret = err;
   1600	}
   1601
   1602	/*
   1603	 * If the inode has dirty timestamps and we need to write them, call
   1604	 * mark_inode_dirty_sync() to notify the filesystem about it and to
   1605	 * change I_DIRTY_TIME into I_DIRTY_SYNC.
   1606	 */
   1607	if ((inode->i_state & I_DIRTY_TIME) &&
   1608	    (wbc->sync_mode == WB_SYNC_ALL ||
   1609	     time_after(jiffies, inode->dirtied_time_when +
   1610			dirtytime_expire_interval * HZ))) {
   1611		trace_writeback_lazytime(inode);
   1612		mark_inode_dirty_sync(inode);
   1613	}
   1614
   1615	/*
   1616	 * Get and clear the dirty flags from i_state.  This needs to be done
   1617	 * after calling writepages because some filesystems may redirty the
   1618	 * inode during writepages due to delalloc.  It also needs to be done
   1619	 * after handling timestamp expiration, as that may dirty the inode too.
   1620	 */
   1621	spin_lock(&inode->i_lock);
   1622	dirty = inode->i_state & I_DIRTY;
   1623	inode->i_state &= ~dirty;
   1624
   1625	/*
   1626	 * Paired with smp_mb() in __mark_inode_dirty().  This allows
   1627	 * __mark_inode_dirty() to test i_state without grabbing i_lock -
   1628	 * either they see the I_DIRTY bits cleared or we see the dirtied
   1629	 * inode.
   1630	 *
   1631	 * I_DIRTY_PAGES is always cleared together above even if @mapping
   1632	 * still has dirty pages.  The flag is reinstated after smp_mb() if
   1633	 * necessary.  This guarantees that either __mark_inode_dirty()
   1634	 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
   1635	 */
   1636	smp_mb();
   1637
   1638	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
   1639		inode->i_state |= I_DIRTY_PAGES;
   1640	else if (unlikely(inode->i_state & I_PINNING_FSCACHE_WB)) {
   1641		if (!(inode->i_state & I_DIRTY_PAGES)) {
   1642			inode->i_state &= ~I_PINNING_FSCACHE_WB;
   1643			wbc->unpinned_fscache_wb = true;
   1644			dirty |= I_PINNING_FSCACHE_WB; /* Cause write_inode */
   1645		}
   1646	}
   1647
   1648	spin_unlock(&inode->i_lock);
   1649
   1650	/* Don't write the inode if only I_DIRTY_PAGES was set */
   1651	if (dirty & ~I_DIRTY_PAGES) {
   1652		int err = write_inode(inode, wbc);
   1653		if (ret == 0)
   1654			ret = err;
   1655	}
   1656	wbc->unpinned_fscache_wb = false;
   1657	trace_writeback_single_inode(inode, wbc, nr_to_write);
   1658	return ret;
   1659}
   1660
   1661/*
   1662 * Write out an inode's dirty data and metadata on-demand, i.e. separately from
   1663 * the regular batched writeback done by the flusher threads in
   1664 * writeback_sb_inodes().  @wbc controls various aspects of the write, such as
   1665 * whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
   1666 *
   1667 * To prevent the inode from going away, either the caller must have a reference
   1668 * to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
   1669 */
   1670static int writeback_single_inode(struct inode *inode,
   1671				  struct writeback_control *wbc)
   1672{
   1673	struct bdi_writeback *wb;
   1674	int ret = 0;
   1675
   1676	spin_lock(&inode->i_lock);
   1677	if (!atomic_read(&inode->i_count))
   1678		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
   1679	else
   1680		WARN_ON(inode->i_state & I_WILL_FREE);
   1681
   1682	if (inode->i_state & I_SYNC) {
   1683		/*
   1684		 * Writeback is already running on the inode.  For WB_SYNC_NONE,
   1685		 * that's enough and we can just return.  For WB_SYNC_ALL, we
   1686		 * must wait for the existing writeback to complete, then do
   1687		 * writeback again if there's anything left.
   1688		 */
   1689		if (wbc->sync_mode != WB_SYNC_ALL)
   1690			goto out;
   1691		__inode_wait_for_writeback(inode);
   1692	}
   1693	WARN_ON(inode->i_state & I_SYNC);
   1694	/*
   1695	 * If the inode is already fully clean, then there's nothing to do.
   1696	 *
   1697	 * For data-integrity syncs we also need to check whether any pages are
   1698	 * still under writeback, e.g. due to prior WB_SYNC_NONE writeback.  If
   1699	 * there are any such pages, we'll need to wait for them.
   1700	 */
   1701	if (!(inode->i_state & I_DIRTY_ALL) &&
   1702	    (wbc->sync_mode != WB_SYNC_ALL ||
   1703	     !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
   1704		goto out;
   1705	inode->i_state |= I_SYNC;
   1706	wbc_attach_and_unlock_inode(wbc, inode);
   1707
   1708	ret = __writeback_single_inode(inode, wbc);
   1709
   1710	wbc_detach_inode(wbc);
   1711
   1712	wb = inode_to_wb_and_lock_list(inode);
   1713	spin_lock(&inode->i_lock);
   1714	/*
   1715	 * If the inode is now fully clean, then it can be safely removed from
   1716	 * its writeback list (if any).  Otherwise the flusher threads are
   1717	 * responsible for the writeback lists.
   1718	 */
   1719	if (!(inode->i_state & I_DIRTY_ALL))
   1720		inode_cgwb_move_to_attached(inode, wb);
   1721	else if (!(inode->i_state & I_SYNC_QUEUED) &&
   1722		 (inode->i_state & I_DIRTY))
   1723		redirty_tail_locked(inode, wb);
   1724
   1725	spin_unlock(&wb->list_lock);
   1726	inode_sync_complete(inode);
   1727out:
   1728	spin_unlock(&inode->i_lock);
   1729	return ret;
   1730}
   1731
   1732static long writeback_chunk_size(struct bdi_writeback *wb,
   1733				 struct wb_writeback_work *work)
   1734{
   1735	long pages;
   1736
   1737	/*
   1738	 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
   1739	 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
   1740	 * here avoids calling into writeback_inodes_wb() more than once.
   1741	 *
   1742	 * The intended call sequence for WB_SYNC_ALL writeback is:
   1743	 *
   1744	 *      wb_writeback()
   1745	 *          writeback_sb_inodes()       <== called only once
   1746	 *              write_cache_pages()     <== called once for each inode
   1747	 *                   (quickly) tag currently dirty pages
   1748	 *                   (maybe slowly) sync all tagged pages
   1749	 */
   1750	if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
   1751		pages = LONG_MAX;
   1752	else {
   1753		pages = min(wb->avg_write_bandwidth / 2,
   1754			    global_wb_domain.dirty_limit / DIRTY_SCOPE);
   1755		pages = min(pages, work->nr_pages);
   1756		pages = round_down(pages + MIN_WRITEBACK_PAGES,
   1757				   MIN_WRITEBACK_PAGES);
   1758	}
   1759
   1760	return pages;
   1761}
   1762
   1763/*
   1764 * Write a portion of b_io inodes which belong to @sb.
   1765 *
   1766 * Return the number of pages and/or inodes written.
   1767 *
   1768 * NOTE! This is called with wb->list_lock held, and will
   1769 * unlock and relock that for each inode it ends up doing
   1770 * IO for.
   1771 */
   1772static long writeback_sb_inodes(struct super_block *sb,
   1773				struct bdi_writeback *wb,
   1774				struct wb_writeback_work *work)
   1775{
   1776	struct writeback_control wbc = {
   1777		.sync_mode		= work->sync_mode,
   1778		.tagged_writepages	= work->tagged_writepages,
   1779		.for_kupdate		= work->for_kupdate,
   1780		.for_background		= work->for_background,
   1781		.for_sync		= work->for_sync,
   1782		.range_cyclic		= work->range_cyclic,
   1783		.range_start		= 0,
   1784		.range_end		= LLONG_MAX,
   1785	};
   1786	unsigned long start_time = jiffies;
   1787	long write_chunk;
   1788	long total_wrote = 0;  /* count both pages and inodes */
   1789
   1790	while (!list_empty(&wb->b_io)) {
   1791		struct inode *inode = wb_inode(wb->b_io.prev);
   1792		struct bdi_writeback *tmp_wb;
   1793		long wrote;
   1794
   1795		if (inode->i_sb != sb) {
   1796			if (work->sb) {
   1797				/*
   1798				 * We only want to write back data for this
   1799				 * superblock, move all inodes not belonging
   1800				 * to it back onto the dirty list.
   1801				 */
   1802				redirty_tail(inode, wb);
   1803				continue;
   1804			}
   1805
   1806			/*
   1807			 * The inode belongs to a different superblock.
   1808			 * Bounce back to the caller to unpin this and
   1809			 * pin the next superblock.
   1810			 */
   1811			break;
   1812		}
   1813
   1814		/*
   1815		 * Don't bother with new inodes or inodes being freed, first
   1816		 * kind does not need periodic writeout yet, and for the latter
   1817		 * kind writeout is handled by the freer.
   1818		 */
   1819		spin_lock(&inode->i_lock);
   1820		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
   1821			redirty_tail_locked(inode, wb);
   1822			spin_unlock(&inode->i_lock);
   1823			continue;
   1824		}
   1825		if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
   1826			/*
   1827			 * If this inode is locked for writeback and we are not
   1828			 * doing writeback-for-data-integrity, move it to
   1829			 * b_more_io so that writeback can proceed with the
   1830			 * other inodes on s_io.
   1831			 *
   1832			 * We'll have another go at writing back this inode
   1833			 * when we completed a full scan of b_io.
   1834			 */
   1835			requeue_io(inode, wb);
   1836			spin_unlock(&inode->i_lock);
   1837			trace_writeback_sb_inodes_requeue(inode);
   1838			continue;
   1839		}
   1840		spin_unlock(&wb->list_lock);
   1841
   1842		/*
   1843		 * We already requeued the inode if it had I_SYNC set and we
   1844		 * are doing WB_SYNC_NONE writeback. So this catches only the
   1845		 * WB_SYNC_ALL case.
   1846		 */
   1847		if (inode->i_state & I_SYNC) {
   1848			/* Wait for I_SYNC. This function drops i_lock... */
   1849			inode_sleep_on_writeback(inode);
   1850			/* Inode may be gone, start again */
   1851			spin_lock(&wb->list_lock);
   1852			continue;
   1853		}
   1854		inode->i_state |= I_SYNC;
   1855		wbc_attach_and_unlock_inode(&wbc, inode);
   1856
   1857		write_chunk = writeback_chunk_size(wb, work);
   1858		wbc.nr_to_write = write_chunk;
   1859		wbc.pages_skipped = 0;
   1860
   1861		/*
   1862		 * We use I_SYNC to pin the inode in memory. While it is set
   1863		 * evict_inode() will wait so the inode cannot be freed.
   1864		 */
   1865		__writeback_single_inode(inode, &wbc);
   1866
   1867		wbc_detach_inode(&wbc);
   1868		work->nr_pages -= write_chunk - wbc.nr_to_write;
   1869		wrote = write_chunk - wbc.nr_to_write - wbc.pages_skipped;
   1870		wrote = wrote < 0 ? 0 : wrote;
   1871		total_wrote += wrote;
   1872
   1873		if (need_resched()) {
   1874			/*
   1875			 * We're trying to balance between building up a nice
   1876			 * long list of IOs to improve our merge rate, and
   1877			 * getting those IOs out quickly for anyone throttling
   1878			 * in balance_dirty_pages().  cond_resched() doesn't
   1879			 * unplug, so get our IOs out the door before we
   1880			 * give up the CPU.
   1881			 */
   1882			blk_flush_plug(current->plug, false);
   1883			cond_resched();
   1884		}
   1885
   1886		/*
   1887		 * Requeue @inode if still dirty.  Be careful as @inode may
   1888		 * have been switched to another wb in the meantime.
   1889		 */
   1890		tmp_wb = inode_to_wb_and_lock_list(inode);
   1891		spin_lock(&inode->i_lock);
   1892		if (!(inode->i_state & I_DIRTY_ALL))
   1893			total_wrote++;
   1894		requeue_inode(inode, tmp_wb, &wbc);
   1895		inode_sync_complete(inode);
   1896		spin_unlock(&inode->i_lock);
   1897
   1898		if (unlikely(tmp_wb != wb)) {
   1899			spin_unlock(&tmp_wb->list_lock);
   1900			spin_lock(&wb->list_lock);
   1901		}
   1902
   1903		/*
   1904		 * bail out to wb_writeback() often enough to check
   1905		 * background threshold and other termination conditions.
   1906		 */
   1907		if (total_wrote) {
   1908			if (time_is_before_jiffies(start_time + HZ / 10UL))
   1909				break;
   1910			if (work->nr_pages <= 0)
   1911				break;
   1912		}
   1913	}
   1914	return total_wrote;
   1915}
   1916
   1917static long __writeback_inodes_wb(struct bdi_writeback *wb,
   1918				  struct wb_writeback_work *work)
   1919{
   1920	unsigned long start_time = jiffies;
   1921	long wrote = 0;
   1922
   1923	while (!list_empty(&wb->b_io)) {
   1924		struct inode *inode = wb_inode(wb->b_io.prev);
   1925		struct super_block *sb = inode->i_sb;
   1926
   1927		if (!trylock_super(sb)) {
   1928			/*
   1929			 * trylock_super() may fail consistently due to
   1930			 * s_umount being grabbed by someone else. Don't use
   1931			 * requeue_io() to avoid busy retrying the inode/sb.
   1932			 */
   1933			redirty_tail(inode, wb);
   1934			continue;
   1935		}
   1936		wrote += writeback_sb_inodes(sb, wb, work);
   1937		up_read(&sb->s_umount);
   1938
   1939		/* refer to the same tests at the end of writeback_sb_inodes */
   1940		if (wrote) {
   1941			if (time_is_before_jiffies(start_time + HZ / 10UL))
   1942				break;
   1943			if (work->nr_pages <= 0)
   1944				break;
   1945		}
   1946	}
   1947	/* Leave any unwritten inodes on b_io */
   1948	return wrote;
   1949}
   1950
   1951static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
   1952				enum wb_reason reason)
   1953{
   1954	struct wb_writeback_work work = {
   1955		.nr_pages	= nr_pages,
   1956		.sync_mode	= WB_SYNC_NONE,
   1957		.range_cyclic	= 1,
   1958		.reason		= reason,
   1959	};
   1960	struct blk_plug plug;
   1961
   1962	blk_start_plug(&plug);
   1963	spin_lock(&wb->list_lock);
   1964	if (list_empty(&wb->b_io))
   1965		queue_io(wb, &work, jiffies);
   1966	__writeback_inodes_wb(wb, &work);
   1967	spin_unlock(&wb->list_lock);
   1968	blk_finish_plug(&plug);
   1969
   1970	return nr_pages - work.nr_pages;
   1971}
   1972
   1973/*
   1974 * Explicit flushing or periodic writeback of "old" data.
   1975 *
   1976 * Define "old": the first time one of an inode's pages is dirtied, we mark the
   1977 * dirtying-time in the inode's address_space.  So this periodic writeback code
   1978 * just walks the superblock inode list, writing back any inodes which are
   1979 * older than a specific point in time.
   1980 *
   1981 * Try to run once per dirty_writeback_interval.  But if a writeback event
   1982 * takes longer than a dirty_writeback_interval interval, then leave a
   1983 * one-second gap.
   1984 *
   1985 * dirtied_before takes precedence over nr_to_write.  So we'll only write back
   1986 * all dirty pages if they are all attached to "old" mappings.
   1987 */
   1988static long wb_writeback(struct bdi_writeback *wb,
   1989			 struct wb_writeback_work *work)
   1990{
   1991	long nr_pages = work->nr_pages;
   1992	unsigned long dirtied_before = jiffies;
   1993	struct inode *inode;
   1994	long progress;
   1995	struct blk_plug plug;
   1996
   1997	blk_start_plug(&plug);
   1998	spin_lock(&wb->list_lock);
   1999	for (;;) {
   2000		/*
   2001		 * Stop writeback when nr_pages has been consumed
   2002		 */
   2003		if (work->nr_pages <= 0)
   2004			break;
   2005
   2006		/*
   2007		 * Background writeout and kupdate-style writeback may
   2008		 * run forever. Stop them if there is other work to do
   2009		 * so that e.g. sync can proceed. They'll be restarted
   2010		 * after the other works are all done.
   2011		 */
   2012		if ((work->for_background || work->for_kupdate) &&
   2013		    !list_empty(&wb->work_list))
   2014			break;
   2015
   2016		/*
   2017		 * For background writeout, stop when we are below the
   2018		 * background dirty threshold
   2019		 */
   2020		if (work->for_background && !wb_over_bg_thresh(wb))
   2021			break;
   2022
   2023		/*
   2024		 * Kupdate and background works are special and we want to
   2025		 * include all inodes that need writing. Livelock avoidance is
   2026		 * handled by these works yielding to any other work so we are
   2027		 * safe.
   2028		 */
   2029		if (work->for_kupdate) {
   2030			dirtied_before = jiffies -
   2031				msecs_to_jiffies(dirty_expire_interval * 10);
   2032		} else if (work->for_background)
   2033			dirtied_before = jiffies;
   2034
   2035		trace_writeback_start(wb, work);
   2036		if (list_empty(&wb->b_io))
   2037			queue_io(wb, work, dirtied_before);
   2038		if (work->sb)
   2039			progress = writeback_sb_inodes(work->sb, wb, work);
   2040		else
   2041			progress = __writeback_inodes_wb(wb, work);
   2042		trace_writeback_written(wb, work);
   2043
   2044		/*
   2045		 * Did we write something? Try for more
   2046		 *
   2047		 * Dirty inodes are moved to b_io for writeback in batches.
   2048		 * The completion of the current batch does not necessarily
   2049		 * mean the overall work is done. So we keep looping as long
   2050		 * as made some progress on cleaning pages or inodes.
   2051		 */
   2052		if (progress)
   2053			continue;
   2054		/*
   2055		 * No more inodes for IO, bail
   2056		 */
   2057		if (list_empty(&wb->b_more_io))
   2058			break;
   2059		/*
   2060		 * Nothing written. Wait for some inode to
   2061		 * become available for writeback. Otherwise
   2062		 * we'll just busyloop.
   2063		 */
   2064		trace_writeback_wait(wb, work);
   2065		inode = wb_inode(wb->b_more_io.prev);
   2066		spin_lock(&inode->i_lock);
   2067		spin_unlock(&wb->list_lock);
   2068		/* This function drops i_lock... */
   2069		inode_sleep_on_writeback(inode);
   2070		spin_lock(&wb->list_lock);
   2071	}
   2072	spin_unlock(&wb->list_lock);
   2073	blk_finish_plug(&plug);
   2074
   2075	return nr_pages - work->nr_pages;
   2076}
   2077
   2078/*
   2079 * Return the next wb_writeback_work struct that hasn't been processed yet.
   2080 */
   2081static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
   2082{
   2083	struct wb_writeback_work *work = NULL;
   2084
   2085	spin_lock_bh(&wb->work_lock);
   2086	if (!list_empty(&wb->work_list)) {
   2087		work = list_entry(wb->work_list.next,
   2088				  struct wb_writeback_work, list);
   2089		list_del_init(&work->list);
   2090	}
   2091	spin_unlock_bh(&wb->work_lock);
   2092	return work;
   2093}
   2094
   2095static long wb_check_background_flush(struct bdi_writeback *wb)
   2096{
   2097	if (wb_over_bg_thresh(wb)) {
   2098
   2099		struct wb_writeback_work work = {
   2100			.nr_pages	= LONG_MAX,
   2101			.sync_mode	= WB_SYNC_NONE,
   2102			.for_background	= 1,
   2103			.range_cyclic	= 1,
   2104			.reason		= WB_REASON_BACKGROUND,
   2105		};
   2106
   2107		return wb_writeback(wb, &work);
   2108	}
   2109
   2110	return 0;
   2111}
   2112
   2113static long wb_check_old_data_flush(struct bdi_writeback *wb)
   2114{
   2115	unsigned long expired;
   2116	long nr_pages;
   2117
   2118	/*
   2119	 * When set to zero, disable periodic writeback
   2120	 */
   2121	if (!dirty_writeback_interval)
   2122		return 0;
   2123
   2124	expired = wb->last_old_flush +
   2125			msecs_to_jiffies(dirty_writeback_interval * 10);
   2126	if (time_before(jiffies, expired))
   2127		return 0;
   2128
   2129	wb->last_old_flush = jiffies;
   2130	nr_pages = get_nr_dirty_pages();
   2131
   2132	if (nr_pages) {
   2133		struct wb_writeback_work work = {
   2134			.nr_pages	= nr_pages,
   2135			.sync_mode	= WB_SYNC_NONE,
   2136			.for_kupdate	= 1,
   2137			.range_cyclic	= 1,
   2138			.reason		= WB_REASON_PERIODIC,
   2139		};
   2140
   2141		return wb_writeback(wb, &work);
   2142	}
   2143
   2144	return 0;
   2145}
   2146
   2147static long wb_check_start_all(struct bdi_writeback *wb)
   2148{
   2149	long nr_pages;
   2150
   2151	if (!test_bit(WB_start_all, &wb->state))
   2152		return 0;
   2153
   2154	nr_pages = get_nr_dirty_pages();
   2155	if (nr_pages) {
   2156		struct wb_writeback_work work = {
   2157			.nr_pages	= wb_split_bdi_pages(wb, nr_pages),
   2158			.sync_mode	= WB_SYNC_NONE,
   2159			.range_cyclic	= 1,
   2160			.reason		= wb->start_all_reason,
   2161		};
   2162
   2163		nr_pages = wb_writeback(wb, &work);
   2164	}
   2165
   2166	clear_bit(WB_start_all, &wb->state);
   2167	return nr_pages;
   2168}
   2169
   2170
   2171/*
   2172 * Retrieve work items and do the writeback they describe
   2173 */
   2174static long wb_do_writeback(struct bdi_writeback *wb)
   2175{
   2176	struct wb_writeback_work *work;
   2177	long wrote = 0;
   2178
   2179	set_bit(WB_writeback_running, &wb->state);
   2180	while ((work = get_next_work_item(wb)) != NULL) {
   2181		trace_writeback_exec(wb, work);
   2182		wrote += wb_writeback(wb, work);
   2183		finish_writeback_work(wb, work);
   2184	}
   2185
   2186	/*
   2187	 * Check for a flush-everything request
   2188	 */
   2189	wrote += wb_check_start_all(wb);
   2190
   2191	/*
   2192	 * Check for periodic writeback, kupdated() style
   2193	 */
   2194	wrote += wb_check_old_data_flush(wb);
   2195	wrote += wb_check_background_flush(wb);
   2196	clear_bit(WB_writeback_running, &wb->state);
   2197
   2198	return wrote;
   2199}
   2200
   2201/*
   2202 * Handle writeback of dirty data for the device backed by this bdi. Also
   2203 * reschedules periodically and does kupdated style flushing.
   2204 */
   2205void wb_workfn(struct work_struct *work)
   2206{
   2207	struct bdi_writeback *wb = container_of(to_delayed_work(work),
   2208						struct bdi_writeback, dwork);
   2209	long pages_written;
   2210
   2211	set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
   2212
   2213	if (likely(!current_is_workqueue_rescuer() ||
   2214		   !test_bit(WB_registered, &wb->state))) {
   2215		/*
   2216		 * The normal path.  Keep writing back @wb until its
   2217		 * work_list is empty.  Note that this path is also taken
   2218		 * if @wb is shutting down even when we're running off the
   2219		 * rescuer as work_list needs to be drained.
   2220		 */
   2221		do {
   2222			pages_written = wb_do_writeback(wb);
   2223			trace_writeback_pages_written(pages_written);
   2224		} while (!list_empty(&wb->work_list));
   2225	} else {
   2226		/*
   2227		 * bdi_wq can't get enough workers and we're running off
   2228		 * the emergency worker.  Don't hog it.  Hopefully, 1024 is
   2229		 * enough for efficient IO.
   2230		 */
   2231		pages_written = writeback_inodes_wb(wb, 1024,
   2232						    WB_REASON_FORKER_THREAD);
   2233		trace_writeback_pages_written(pages_written);
   2234	}
   2235
   2236	if (!list_empty(&wb->work_list))
   2237		wb_wakeup(wb);
   2238	else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
   2239		wb_wakeup_delayed(wb);
   2240}
   2241
   2242/*
   2243 * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
   2244 * write back the whole world.
   2245 */
   2246static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
   2247					 enum wb_reason reason)
   2248{
   2249	struct bdi_writeback *wb;
   2250
   2251	if (!bdi_has_dirty_io(bdi))
   2252		return;
   2253
   2254	list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
   2255		wb_start_writeback(wb, reason);
   2256}
   2257
   2258void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
   2259				enum wb_reason reason)
   2260{
   2261	rcu_read_lock();
   2262	__wakeup_flusher_threads_bdi(bdi, reason);
   2263	rcu_read_unlock();
   2264}
   2265
   2266/*
   2267 * Wakeup the flusher threads to start writeback of all currently dirty pages
   2268 */
   2269void wakeup_flusher_threads(enum wb_reason reason)
   2270{
   2271	struct backing_dev_info *bdi;
   2272
   2273	/*
   2274	 * If we are expecting writeback progress we must submit plugged IO.
   2275	 */
   2276	blk_flush_plug(current->plug, true);
   2277
   2278	rcu_read_lock();
   2279	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
   2280		__wakeup_flusher_threads_bdi(bdi, reason);
   2281	rcu_read_unlock();
   2282}
   2283
   2284/*
   2285 * Wake up bdi's periodically to make sure dirtytime inodes gets
   2286 * written back periodically.  We deliberately do *not* check the
   2287 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
   2288 * kernel to be constantly waking up once there are any dirtytime
   2289 * inodes on the system.  So instead we define a separate delayed work
   2290 * function which gets called much more rarely.  (By default, only
   2291 * once every 12 hours.)
   2292 *
   2293 * If there is any other write activity going on in the file system,
   2294 * this function won't be necessary.  But if the only thing that has
   2295 * happened on the file system is a dirtytime inode caused by an atime
   2296 * update, we need this infrastructure below to make sure that inode
   2297 * eventually gets pushed out to disk.
   2298 */
   2299static void wakeup_dirtytime_writeback(struct work_struct *w);
   2300static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
   2301
   2302static void wakeup_dirtytime_writeback(struct work_struct *w)
   2303{
   2304	struct backing_dev_info *bdi;
   2305
   2306	rcu_read_lock();
   2307	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
   2308		struct bdi_writeback *wb;
   2309
   2310		list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
   2311			if (!list_empty(&wb->b_dirty_time))
   2312				wb_wakeup(wb);
   2313	}
   2314	rcu_read_unlock();
   2315	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
   2316}
   2317
   2318static int __init start_dirtytime_writeback(void)
   2319{
   2320	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
   2321	return 0;
   2322}
   2323__initcall(start_dirtytime_writeback);
   2324
   2325int dirtytime_interval_handler(struct ctl_table *table, int write,
   2326			       void *buffer, size_t *lenp, loff_t *ppos)
   2327{
   2328	int ret;
   2329
   2330	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
   2331	if (ret == 0 && write)
   2332		mod_delayed_work(system_wq, &dirtytime_work, 0);
   2333	return ret;
   2334}
   2335
   2336/**
   2337 * __mark_inode_dirty -	internal function to mark an inode dirty
   2338 *
   2339 * @inode: inode to mark
   2340 * @flags: what kind of dirty, e.g. I_DIRTY_SYNC.  This can be a combination of
   2341 *	   multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
   2342 *	   with I_DIRTY_PAGES.
   2343 *
   2344 * Mark an inode as dirty.  We notify the filesystem, then update the inode's
   2345 * dirty flags.  Then, if needed we add the inode to the appropriate dirty list.
   2346 *
   2347 * Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
   2348 * instead of calling this directly.
   2349 *
   2350 * CAREFUL!  We only add the inode to the dirty list if it is hashed or if it
   2351 * refers to a blockdev.  Unhashed inodes will never be added to the dirty list
   2352 * even if they are later hashed, as they will have been marked dirty already.
   2353 *
   2354 * In short, ensure you hash any inodes _before_ you start marking them dirty.
   2355 *
   2356 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
   2357 * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
   2358 * the kernel-internal blockdev inode represents the dirtying time of the
   2359 * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
   2360 * page->mapping->host, so the page-dirtying time is recorded in the internal
   2361 * blockdev inode.
   2362 */
   2363void __mark_inode_dirty(struct inode *inode, int flags)
   2364{
   2365	struct super_block *sb = inode->i_sb;
   2366	int dirtytime = 0;
   2367	struct bdi_writeback *wb = NULL;
   2368
   2369	trace_writeback_mark_inode_dirty(inode, flags);
   2370
   2371	if (flags & I_DIRTY_INODE) {
   2372		/*
   2373		 * Notify the filesystem about the inode being dirtied, so that
   2374		 * (if needed) it can update on-disk fields and journal the
   2375		 * inode.  This is only needed when the inode itself is being
   2376		 * dirtied now.  I.e. it's only needed for I_DIRTY_INODE, not
   2377		 * for just I_DIRTY_PAGES or I_DIRTY_TIME.
   2378		 */
   2379		trace_writeback_dirty_inode_start(inode, flags);
   2380		if (sb->s_op->dirty_inode)
   2381			sb->s_op->dirty_inode(inode, flags & I_DIRTY_INODE);
   2382		trace_writeback_dirty_inode(inode, flags);
   2383
   2384		/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
   2385		flags &= ~I_DIRTY_TIME;
   2386	} else {
   2387		/*
   2388		 * Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
   2389		 * (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
   2390		 * in one call to __mark_inode_dirty().)
   2391		 */
   2392		dirtytime = flags & I_DIRTY_TIME;
   2393		WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
   2394	}
   2395
   2396	/*
   2397	 * Paired with smp_mb() in __writeback_single_inode() for the
   2398	 * following lockless i_state test.  See there for details.
   2399	 */
   2400	smp_mb();
   2401
   2402	if (((inode->i_state & flags) == flags) ||
   2403	    (dirtytime && (inode->i_state & I_DIRTY_INODE)))
   2404		return;
   2405
   2406	spin_lock(&inode->i_lock);
   2407	if (dirtytime && (inode->i_state & I_DIRTY_INODE))
   2408		goto out_unlock_inode;
   2409	if ((inode->i_state & flags) != flags) {
   2410		const int was_dirty = inode->i_state & I_DIRTY;
   2411
   2412		inode_attach_wb(inode, NULL);
   2413
   2414		/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
   2415		if (flags & I_DIRTY_INODE)
   2416			inode->i_state &= ~I_DIRTY_TIME;
   2417		inode->i_state |= flags;
   2418
   2419		/*
   2420		 * Grab inode's wb early because it requires dropping i_lock and we
   2421		 * need to make sure following checks happen atomically with dirty
   2422		 * list handling so that we don't move inodes under flush worker's
   2423		 * hands.
   2424		 */
   2425		if (!was_dirty) {
   2426			wb = locked_inode_to_wb_and_lock_list(inode);
   2427			spin_lock(&inode->i_lock);
   2428		}
   2429
   2430		/*
   2431		 * If the inode is queued for writeback by flush worker, just
   2432		 * update its dirty state. Once the flush worker is done with
   2433		 * the inode it will place it on the appropriate superblock
   2434		 * list, based upon its state.
   2435		 */
   2436		if (inode->i_state & I_SYNC_QUEUED)
   2437			goto out_unlock;
   2438
   2439		/*
   2440		 * Only add valid (hashed) inodes to the superblock's
   2441		 * dirty list.  Add blockdev inodes as well.
   2442		 */
   2443		if (!S_ISBLK(inode->i_mode)) {
   2444			if (inode_unhashed(inode))
   2445				goto out_unlock;
   2446		}
   2447		if (inode->i_state & I_FREEING)
   2448			goto out_unlock;
   2449
   2450		/*
   2451		 * If the inode was already on b_dirty/b_io/b_more_io, don't
   2452		 * reposition it (that would break b_dirty time-ordering).
   2453		 */
   2454		if (!was_dirty) {
   2455			struct list_head *dirty_list;
   2456			bool wakeup_bdi = false;
   2457
   2458			inode->dirtied_when = jiffies;
   2459			if (dirtytime)
   2460				inode->dirtied_time_when = jiffies;
   2461
   2462			if (inode->i_state & I_DIRTY)
   2463				dirty_list = &wb->b_dirty;
   2464			else
   2465				dirty_list = &wb->b_dirty_time;
   2466
   2467			wakeup_bdi = inode_io_list_move_locked(inode, wb,
   2468							       dirty_list);
   2469
   2470			spin_unlock(&wb->list_lock);
   2471			spin_unlock(&inode->i_lock);
   2472			trace_writeback_dirty_inode_enqueue(inode);
   2473
   2474			/*
   2475			 * If this is the first dirty inode for this bdi,
   2476			 * we have to wake-up the corresponding bdi thread
   2477			 * to make sure background write-back happens
   2478			 * later.
   2479			 */
   2480			if (wakeup_bdi &&
   2481			    (wb->bdi->capabilities & BDI_CAP_WRITEBACK))
   2482				wb_wakeup_delayed(wb);
   2483			return;
   2484		}
   2485	}
   2486out_unlock:
   2487	if (wb)
   2488		spin_unlock(&wb->list_lock);
   2489out_unlock_inode:
   2490	spin_unlock(&inode->i_lock);
   2491}
   2492EXPORT_SYMBOL(__mark_inode_dirty);
   2493
   2494/*
   2495 * The @s_sync_lock is used to serialise concurrent sync operations
   2496 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
   2497 * Concurrent callers will block on the s_sync_lock rather than doing contending
   2498 * walks. The queueing maintains sync(2) required behaviour as all the IO that
   2499 * has been issued up to the time this function is enter is guaranteed to be
   2500 * completed by the time we have gained the lock and waited for all IO that is
   2501 * in progress regardless of the order callers are granted the lock.
   2502 */
   2503static void wait_sb_inodes(struct super_block *sb)
   2504{
   2505	LIST_HEAD(sync_list);
   2506
   2507	/*
   2508	 * We need to be protected against the filesystem going from
   2509	 * r/o to r/w or vice versa.
   2510	 */
   2511	WARN_ON(!rwsem_is_locked(&sb->s_umount));
   2512
   2513	mutex_lock(&sb->s_sync_lock);
   2514
   2515	/*
   2516	 * Splice the writeback list onto a temporary list to avoid waiting on
   2517	 * inodes that have started writeback after this point.
   2518	 *
   2519	 * Use rcu_read_lock() to keep the inodes around until we have a
   2520	 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
   2521	 * the local list because inodes can be dropped from either by writeback
   2522	 * completion.
   2523	 */
   2524	rcu_read_lock();
   2525	spin_lock_irq(&sb->s_inode_wblist_lock);
   2526	list_splice_init(&sb->s_inodes_wb, &sync_list);
   2527
   2528	/*
   2529	 * Data integrity sync. Must wait for all pages under writeback, because
   2530	 * there may have been pages dirtied before our sync call, but which had
   2531	 * writeout started before we write it out.  In which case, the inode
   2532	 * may not be on the dirty list, but we still have to wait for that
   2533	 * writeout.
   2534	 */
   2535	while (!list_empty(&sync_list)) {
   2536		struct inode *inode = list_first_entry(&sync_list, struct inode,
   2537						       i_wb_list);
   2538		struct address_space *mapping = inode->i_mapping;
   2539
   2540		/*
   2541		 * Move each inode back to the wb list before we drop the lock
   2542		 * to preserve consistency between i_wb_list and the mapping
   2543		 * writeback tag. Writeback completion is responsible to remove
   2544		 * the inode from either list once the writeback tag is cleared.
   2545		 */
   2546		list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
   2547
   2548		/*
   2549		 * The mapping can appear untagged while still on-list since we
   2550		 * do not have the mapping lock. Skip it here, wb completion
   2551		 * will remove it.
   2552		 */
   2553		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
   2554			continue;
   2555
   2556		spin_unlock_irq(&sb->s_inode_wblist_lock);
   2557
   2558		spin_lock(&inode->i_lock);
   2559		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
   2560			spin_unlock(&inode->i_lock);
   2561
   2562			spin_lock_irq(&sb->s_inode_wblist_lock);
   2563			continue;
   2564		}
   2565		__iget(inode);
   2566		spin_unlock(&inode->i_lock);
   2567		rcu_read_unlock();
   2568
   2569		/*
   2570		 * We keep the error status of individual mapping so that
   2571		 * applications can catch the writeback error using fsync(2).
   2572		 * See filemap_fdatawait_keep_errors() for details.
   2573		 */
   2574		filemap_fdatawait_keep_errors(mapping);
   2575
   2576		cond_resched();
   2577
   2578		iput(inode);
   2579
   2580		rcu_read_lock();
   2581		spin_lock_irq(&sb->s_inode_wblist_lock);
   2582	}
   2583	spin_unlock_irq(&sb->s_inode_wblist_lock);
   2584	rcu_read_unlock();
   2585	mutex_unlock(&sb->s_sync_lock);
   2586}
   2587
   2588static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
   2589				     enum wb_reason reason, bool skip_if_busy)
   2590{
   2591	struct backing_dev_info *bdi = sb->s_bdi;
   2592	DEFINE_WB_COMPLETION(done, bdi);
   2593	struct wb_writeback_work work = {
   2594		.sb			= sb,
   2595		.sync_mode		= WB_SYNC_NONE,
   2596		.tagged_writepages	= 1,
   2597		.done			= &done,
   2598		.nr_pages		= nr,
   2599		.reason			= reason,
   2600	};
   2601
   2602	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
   2603		return;
   2604	WARN_ON(!rwsem_is_locked(&sb->s_umount));
   2605
   2606	bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
   2607	wb_wait_for_completion(&done);
   2608}
   2609
   2610/**
   2611 * writeback_inodes_sb_nr -	writeback dirty inodes from given super_block
   2612 * @sb: the superblock
   2613 * @nr: the number of pages to write
   2614 * @reason: reason why some writeback work initiated
   2615 *
   2616 * Start writeback on some inodes on this super_block. No guarantees are made
   2617 * on how many (if any) will be written, and this function does not wait
   2618 * for IO completion of submitted IO.
   2619 */
   2620void writeback_inodes_sb_nr(struct super_block *sb,
   2621			    unsigned long nr,
   2622			    enum wb_reason reason)
   2623{
   2624	__writeback_inodes_sb_nr(sb, nr, reason, false);
   2625}
   2626EXPORT_SYMBOL(writeback_inodes_sb_nr);
   2627
   2628/**
   2629 * writeback_inodes_sb	-	writeback dirty inodes from given super_block
   2630 * @sb: the superblock
   2631 * @reason: reason why some writeback work was initiated
   2632 *
   2633 * Start writeback on some inodes on this super_block. No guarantees are made
   2634 * on how many (if any) will be written, and this function does not wait
   2635 * for IO completion of submitted IO.
   2636 */
   2637void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
   2638{
   2639	return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
   2640}
   2641EXPORT_SYMBOL(writeback_inodes_sb);
   2642
   2643/**
   2644 * try_to_writeback_inodes_sb - try to start writeback if none underway
   2645 * @sb: the superblock
   2646 * @reason: reason why some writeback work was initiated
   2647 *
   2648 * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
   2649 */
   2650void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
   2651{
   2652	if (!down_read_trylock(&sb->s_umount))
   2653		return;
   2654
   2655	__writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
   2656	up_read(&sb->s_umount);
   2657}
   2658EXPORT_SYMBOL(try_to_writeback_inodes_sb);
   2659
   2660/**
   2661 * sync_inodes_sb	-	sync sb inode pages
   2662 * @sb: the superblock
   2663 *
   2664 * This function writes and waits on any dirty inode belonging to this
   2665 * super_block.
   2666 */
   2667void sync_inodes_sb(struct super_block *sb)
   2668{
   2669	struct backing_dev_info *bdi = sb->s_bdi;
   2670	DEFINE_WB_COMPLETION(done, bdi);
   2671	struct wb_writeback_work work = {
   2672		.sb		= sb,
   2673		.sync_mode	= WB_SYNC_ALL,
   2674		.nr_pages	= LONG_MAX,
   2675		.range_cyclic	= 0,
   2676		.done		= &done,
   2677		.reason		= WB_REASON_SYNC,
   2678		.for_sync	= 1,
   2679	};
   2680
   2681	/*
   2682	 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
   2683	 * inodes under writeback and I_DIRTY_TIME inodes ignored by
   2684	 * bdi_has_dirty() need to be written out too.
   2685	 */
   2686	if (bdi == &noop_backing_dev_info)
   2687		return;
   2688	WARN_ON(!rwsem_is_locked(&sb->s_umount));
   2689
   2690	/* protect against inode wb switch, see inode_switch_wbs_work_fn() */
   2691	bdi_down_write_wb_switch_rwsem(bdi);
   2692	bdi_split_work_to_wbs(bdi, &work, false);
   2693	wb_wait_for_completion(&done);
   2694	bdi_up_write_wb_switch_rwsem(bdi);
   2695
   2696	wait_sb_inodes(sb);
   2697}
   2698EXPORT_SYMBOL(sync_inodes_sb);
   2699
   2700/**
   2701 * write_inode_now	-	write an inode to disk
   2702 * @inode: inode to write to disk
   2703 * @sync: whether the write should be synchronous or not
   2704 *
   2705 * This function commits an inode to disk immediately if it is dirty. This is
   2706 * primarily needed by knfsd.
   2707 *
   2708 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
   2709 */
   2710int write_inode_now(struct inode *inode, int sync)
   2711{
   2712	struct writeback_control wbc = {
   2713		.nr_to_write = LONG_MAX,
   2714		.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
   2715		.range_start = 0,
   2716		.range_end = LLONG_MAX,
   2717	};
   2718
   2719	if (!mapping_can_writeback(inode->i_mapping))
   2720		wbc.nr_to_write = 0;
   2721
   2722	might_sleep();
   2723	return writeback_single_inode(inode, &wbc);
   2724}
   2725EXPORT_SYMBOL(write_inode_now);
   2726
   2727/**
   2728 * sync_inode_metadata - write an inode to disk
   2729 * @inode: the inode to sync
   2730 * @wait: wait for I/O to complete.
   2731 *
   2732 * Write an inode to disk and adjust its dirty state after completion.
   2733 *
   2734 * Note: only writes the actual inode, no associated data or other metadata.
   2735 */
   2736int sync_inode_metadata(struct inode *inode, int wait)
   2737{
   2738	struct writeback_control wbc = {
   2739		.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
   2740		.nr_to_write = 0, /* metadata-only */
   2741	};
   2742
   2743	return writeback_single_inode(inode, &wbc);
   2744}
   2745EXPORT_SYMBOL(sync_inode_metadata);