Messages in this thread Patch in this message | | | From | Darren Hart <> | Subject | [PATCH] futex: add memory barrier commentary to futex_wait_queue_me | Date | Thu, 24 Sep 2009 11:54:47 -0700 |
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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: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@elte.hu> CC: Eric Dumazet <eric.dumazet@gmail.com> CC: Dinakar Guniguntala <dino@in.ibm.com> CC: John Stultz <johnstul@us.ibm.com> ---
kernel/futex.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c index 463af2e..b911adc 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1656,6 +1656,12 @@ out: 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);
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