From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH v2 4/9] completion: Replace spin_unlock_wait() with lock/unlock pair Date: Wed, 5 Jul 2017 16:31:38 -0700 Message-ID: <1499297503-23852-4-git-send-email-paulmck@linux.vnet.ibm.com> References: <20170705232955.GA15992@linux.vnet.ibm.com> Cc: netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, oleg@redhat.com, akpm@linux-foundation.org, mingo@redhat.com, dave@stgolabs.net, manfred@colorfullife.com, tj@kernel.org, arnd@arndb.de, linux-arch@vger.kernel.org, will.deacon@arm.com, peterz@infradead.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, torvalds@linux-foundation.org, "Paul E. McKenney" To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <20170705232955.GA15992@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Alan Stern Cc: Andrea Parri Cc: Linus Torvalds --- 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