Commit 9beba3c5 authored Sep 24, 2009 by Darren Hart Committed by Ingo Molnar Sep 24, 2009

futex: Add memory barrier commentary to futex_wait_queue_me()



The memory barrier semantics of futex_wait_queue_me() are
non-obvious. Add some commentary to try and clarify it.

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Dinakar Guniguntala <dino@in.ibm.com>
Cc: John Stultz <johnstul@us.ibm.com>
LKML-Reference: <20090924185447.694.38948.stgit@Aeon>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 0729e196

kernel/futex.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -1656,6 +1656,12 @@ static int fixup_owner(u32 __user uaddr, int fshared, struct futex_q q,
		static void futex_wait_queue_me(struct futex_hash_bucket hb, struct futex_q q,
		struct hrtimer_sleeper *timeout)
		{
		/*
		* The task state is guaranteed to be set before another task can
		* wake it. set_current_state() is implemented using set_mb() and
		* queue_me() calls spin_unlock() upon completion, both serializing
		* access to the hash list and forcing another memory barrier.
		*/
		set_current_state(TASK_INTERRUPTIBLE);
		queue_me(q, hb);