locking/rwsem: Document barrier need when waking tasks (49e4b2bc) · Commits · 戴 / test

The need for the smp_mb() in __rwsem_do_wake() should be properly documented. Applies to both xadd and spinlock variants. Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Jason Low <jason.low2@hp.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michel Lespinasse <walken@google.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tim Chen <tim.c.chen@linux.intel.com> Link: http://lkml.kernel.org/r/1422609267-15102-3-git-send-email-dave@stgolabs.net Signed-off-by:

kernel/locking/rwsem-spinlock.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -85,6 +85,13 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)

		list_del(&waiter->list);
		tsk = waiter->task;
		/*
		* Make sure we do not wakeup the next reader before
		* setting the nil condition to grant the next reader;
		* otherwise we could miss the wakeup on the other
		* side and end up sleeping again. See the pairing
		* in rwsem_down_read_failed().
		*/
		smp_mb();
		waiter->task = NULL;
		wake_up_process(tsk);

+7 −0

Original line number	Diff line number	Diff line
		@@ -186,6 +186,13 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type)
		waiter = list_entry(next, struct rwsem_waiter, list);
		next = waiter->list.next;
		tsk = waiter->task;
		/*
		* Make sure we do not wakeup the next reader before
		* setting the nil condition to grant the next reader;
		* otherwise we could miss the wakeup on the other
		* side and end up sleeping again. See the pairing
		* in rwsem_down_read_failed().
		*/
		smp_mb();
		waiter->task = NULL;
		wake_up_process(tsk);