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Date: Wed, 5 Jul 2017 16:31:38 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: netfilter-devel@...r.kernel.org, netdev@...r.kernel.org, oleg@...hat.com, akpm@...ux-foundation.org, mingo@...hat.com, dave@...olabs.net, manfred@...orfullife.com, tj@...nel.org, arnd@...db.de, linux-arch@...r.kernel.org, will.deacon@....com, peterz@...radead.org, stern@...land.harvard.edu, parri.andrea@...il.com, torvalds@...ux-foundation.org, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: [PATCH v2 4/9] completion: Replace spin_unlock_wait() with lock/unlock pair There is no agreed-upon definition of spin_unlock_wait()'s semantics, and it appears that all callers could do just as well with a lock/unlock pair. This commit therefore replaces the spin_unlock_wait() call in completion_done() with spin_lock() followed immediately by spin_unlock(). This should be safe from a performance perspective because the lock will be held only the wakeup happens really quickly. Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> Cc: Ingo Molnar <mingo@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Will Deacon <will.deacon@....com> Cc: Alan Stern <stern@...land.harvard.edu> Cc: Andrea Parri <parri.andrea@...il.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org> --- kernel/sched/completion.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c index 53f9558fa925..3e66712e1964 100644 --- a/kernel/sched/completion.c +++ b/kernel/sched/completion.c @@ -307,14 +307,9 @@ bool completion_done(struct completion *x) * If ->done, we need to wait for complete() to release ->wait.lock * otherwise we can end up freeing the completion before complete() * is done referencing it. - * - * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders - * the loads of ->done and ->wait.lock such that we cannot observe - * the lock before complete() acquires it while observing the ->done - * after it's acquired the lock. */ - smp_rmb(); - spin_unlock_wait(&x->wait.lock); + spin_lock_irq(&x->wait.lock); + spin_unlock_irq(&x->wait.lock); return true; } EXPORT_SYMBOL(completion_done); -- 2.5.2
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