Commit 6f568ebe authored Feb 06, 2019 by Davidlohr Bueso Committed by Thomas Gleixner Feb 08, 2019

futex: Fix barrier comment



The current comment for the barrier that guarantees that waiter increment
is always before taking the hb spinlock (barrier (A)) needs to be fixed as
it is misplaced.

This is obviously referring to hb_waiters_inc, which is a full barrier.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190206185602.949-1-dave@stgolabs.net

parent 74e96711

kernel/futex.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -2221,11 +2221,11 @@ static inline struct futex_hash_bucket queue_lock(struct futex_q q)
		* decrement the counter at queue_unlock() when some error has
		* occurred and we don't end up adding the task to the list.
		*/
		hb_waiters_inc(hb);
		hb_waiters_inc(hb); /* implies smp_mb(); (A) */

		q->lock_ptr = &hb->lock;

		spin_lock(&hb->lock); /* implies smp_mb(); (A) */
		spin_lock(&hb->lock);
		return hb;
		}