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Oleg Nesterov authored
Commit de30ec47 "Remove unnecessary ->wait.lock serialization when reading completion state" was not correct, without lock/unlock the code like stop_machine_from_inactive_cpu() while (!completion_done()) cpu_relax(); can return before complete() finishes its spin_unlock() which writes to this memory. And spin_unlock_wait(). While at it, change try_wait_for_completion() to use READ_ONCE(). Reported-by:
Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reported-by:
Davidlohr Bueso <dave@stgolabs.net> Tested-by:
Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by:
Oleg Nesterov <oleg@redhat.com> Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org> [ Added a comment with the barrier. ] Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Nicholas Mc Guire <der.herr@hofr.at> Cc: raghavendra.kt@linux.vnet.ibm.com Cc: waiman.long@hp.com Fixes: de30ec47 ("sched/completion: Remove unnecessary ->wait.lock serialization when reading completion state") Link: http://lkml.kernel.org/r/20150212195913.GA30430@redhat.comSigned-off-by:
Ingo Molnar <mingo@kernel.org>
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