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| author | Nicholas Mc Guire <der.herr@hofr.at> | 2015-01-23 12:41:47 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-02-04 07:57:37 +0100 |
| commit | 7c34e3180a01c800a40bc8535654d5735802fc1b (patch) | |
| tree | 7b2b9408d49b48b4aed1ae94619112da0569ee7e /kernel/sched | |
| parent | de30ec47302c101c7badc8fe687641fd75e596e7 (diff) | |
| download | linux-stable-7c34e3180a01c800a40bc8535654d5735802fc1b.tar.gz linux-stable-7c34e3180a01c800a40bc8535654d5735802fc1b.tar.bz2 linux-stable-7c34e3180a01c800a40bc8535654d5735802fc1b.zip | |
sched/completion: Add lock-free checking of the blocking case
The "thread would block" case can be checked without grabbing ->wait.lock.
[ If the check does not return early then grab the lock and recheck.
A memory barrier is not needed as complete() and complete_all() imply
a barrier.
The ACCESS_ONCE() is needed for calls in a loop that, if inlined, could
optimize out the re-fetching of x->done. ]
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1422013307-13200-1-git-send-email-der.herr@hofr.at
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/completion.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c index 9d1fe32da232..7052d3fd4e7b 100644 --- a/kernel/sched/completion.c +++ b/kernel/sched/completion.c @@ -268,6 +268,15 @@ bool try_wait_for_completion(struct completion *x) unsigned long flags; int ret = 1; + /* + * Since x->done will need to be locked only + * in the non-blocking case, we check x->done + * first without taking the lock so we can + * return early in the blocking case. + */ + if (!ACCESS_ONCE(x->done)) + return 0; + spin_lock_irqsave(&x->wait.lock, flags); if (!x->done) ret = 0; |