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sched/completion: Add lock-free checking of the blocking case
authorNicholas Mc Guire <der.herr@hofr.at>
Fri, 23 Jan 2015 11:41:47 +0000 (12:41 +0100)
committerIngo Molnar <mingo@kernel.org>
Wed, 4 Feb 2015 06:57:37 +0000 (07:57 +0100)
commit7c34e3180a01c800a40bc8535654d5735802fc1b
tree7b2b9408d49b48b4aed1ae94619112da0569ee7e
parentde30ec47302c101c7badc8fe687641fd75e596e7
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>
kernel/sched/completion.c