Commit 99143f82 authored Jul 18, 2019 by Peter Zijlstra Committed by Ingo Molnar Jul 25, 2019

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: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent e1b98fa3

kernel/locking/rwsem.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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)

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