Commit 9beba3c5 authored by Darren Hart's avatar Darren Hart Committed by Ingo Molnar

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: default avatarDarren 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: default avatarIngo Molnar <mingo@elte.hu>
parent 0729e196
...@@ -1656,6 +1656,12 @@ static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q, ...@@ -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, static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
struct hrtimer_sleeper *timeout) 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); set_current_state(TASK_INTERRUPTIBLE);
queue_me(q, hb); queue_me(q, hb);
......
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