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| author | Darren Hart <dvhltc@us.ibm.com> | 2009-09-24 11:54:47 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-09-24 22:30:10 +0200 |
| commit | 9beba3c54dd180a26a1da2027cfbe9edfaf9c40e (patch) | |
| tree | b7ede0a88beb7ee195adf40a7a03140e77ba43ee /kernel | |
| parent | 0729e196147692d84d4c099fcff056eba2ed61d8 (diff) | |
| download | lwn-9beba3c54dd180a26a1da2027cfbe9edfaf9c40e.tar.gz lwn-9beba3c54dd180a26a1da2027cfbe9edfaf9c40e.zip | |
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/futex.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index 463af2efa512..b911adceb2c4 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); |