Commit-ID: 49e4b2bcf7b812e985e65b6c8a0255b1520a6e7e Gitweb: http://git.kernel.org/tip/49e4b2bcf7b812e985e65b6c8a0255b1520a6e7e Author: Davidlohr Bueso <[email protected]> AuthorDate: Fri, 30 Jan 2015 01:14:24 -0800 Committer: Ingo Molnar <[email protected]> CommitDate: Wed, 18 Feb 2015 16:57:10 +0100
locking/rwsem: Document barrier need when waking tasks The need for the smp_mb() in __rwsem_do_wake() should be properly documented. Applies to both xadd and spinlock variants. Signed-off-by: Davidlohr Bueso <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Jason Low <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Michel Lespinasse <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Tim Chen <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- kernel/locking/rwsem-spinlock.c | 7 +++++++ kernel/locking/rwsem-xadd.c | 7 +++++++ 2 files changed, 14 insertions(+) diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c index 2555ae1..3a50485 100644 --- a/kernel/locking/rwsem-spinlock.c +++ b/kernel/locking/rwsem-spinlock.c @@ -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); diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 2f7cc40..82aba46 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
