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lcoking/rwsem: Add missing ACQUIRE to read_slowpath sleep loop 

While reviewing another read_slowpath patch, both Will and I noticed
another missing ACQUIRE, namely:

  X = 0;

  CPU0			CPU1

  rwsem_down_read()
    for (;;) {
      set_current_state(TASK_UNINTERRUPTIBLE);

                        X = 1;
                        rwsem_up_write();
                          rwsem_mark_wake()
                            atomic_long_add(adjustment, &sem->count);
                            smp_store_release(&waiter->task, NULL);

      if (!waiter.task)
        break;

      ...
    }

  r = X;

Allows 'r == 0'.

Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2019-07-18 14:56:17 +02:00 committed by Ingo Molnar
parent e1b98fa316
commit 99143f82a2
1 changed files with 3 additions and 1 deletions
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4
kernel/locking/rwsem.c
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@ -1073,8 +1073,10 @@ queue:
/* wait to be given the lock */
while (true) {
set_current_state(state);
if (!waiter.task)
if (!smp_load_acquire(&waiter.task)) {
/* Orders against rwsem_mark_wake()'s smp_store_release() */
break;
}
if (signal_pending_state(state, current)) {
raw_spin_lock_irq(&sem->wait_lock);
if (waiter.task)