cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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qrwlock.c (2600B)

      1// SPDX-License-Identifier: GPL-2.0-or-later
      2/*
      3 * Queued read/write locks
      4 *
      5 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
      6 *
      7 * Authors: Waiman Long <waiman.long@hp.com>
      8 */
      9#include <linux/smp.h>
     10#include <linux/bug.h>
     11#include <linux/cpumask.h>
     12#include <linux/percpu.h>
     13#include <linux/hardirq.h>
     14#include <linux/spinlock.h>
     15#include <trace/events/lock.h>
     16
     17/**
     18 * queued_read_lock_slowpath - acquire read lock of a queued rwlock
     19 * @lock: Pointer to queued rwlock structure
     20 */
     21void queued_read_lock_slowpath(struct qrwlock *lock)
     22{
     23	/*
     24	 * Readers come here when they cannot get the lock without waiting
     25	 */
     26	if (unlikely(in_interrupt())) {
     27		/*
     28		 * Readers in interrupt context will get the lock immediately
     29		 * if the writer is just waiting (not holding the lock yet),
     30		 * so spin with ACQUIRE semantics until the lock is available
     31		 * without waiting in the queue.
     32		 */
     33		atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
     34		return;
     35	}
     36	atomic_sub(_QR_BIAS, &lock->cnts);
     37
     38	trace_contention_begin(lock, LCB_F_SPIN | LCB_F_READ);
     39
     40	/*
     41	 * Put the reader into the wait queue
     42	 */
     43	arch_spin_lock(&lock->wait_lock);
     44	atomic_add(_QR_BIAS, &lock->cnts);
     45
     46	/*
     47	 * The ACQUIRE semantics of the following spinning code ensure
     48	 * that accesses can't leak upwards out of our subsequent critical
     49	 * section in the case that the lock is currently held for write.
     50	 */
     51	atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
     52
     53	/*
     54	 * Signal the next one in queue to become queue head
     55	 */
     56	arch_spin_unlock(&lock->wait_lock);
     57
     58	trace_contention_end(lock, 0);
     59}
     60EXPORT_SYMBOL(queued_read_lock_slowpath);
     61
     62/**
     63 * queued_write_lock_slowpath - acquire write lock of a queued rwlock
     64 * @lock : Pointer to queued rwlock structure
     65 */
     66void queued_write_lock_slowpath(struct qrwlock *lock)
     67{
     68	int cnts;
     69
     70	trace_contention_begin(lock, LCB_F_SPIN | LCB_F_WRITE);
     71
     72	/* Put the writer into the wait queue */
     73	arch_spin_lock(&lock->wait_lock);
     74
     75	/* Try to acquire the lock directly if no reader is present */
     76	if (!(cnts = atomic_read(&lock->cnts)) &&
     77	    atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED))
     78		goto unlock;
     79
     80	/* Set the waiting flag to notify readers that a writer is pending */
     81	atomic_or(_QW_WAITING, &lock->cnts);
     82
     83	/* When no more readers or writers, set the locked flag */
     84	do {
     85		cnts = atomic_cond_read_relaxed(&lock->cnts, VAL == _QW_WAITING);
     86	} while (!atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED));
     87unlock:
     88	arch_spin_unlock(&lock->wait_lock);
     89
     90	trace_contention_end(lock, 0);
     91}
     92EXPORT_SYMBOL(queued_write_lock_slowpath);