Commit-ID: 1e40c2edef2537f87f94d0baf80aeaeb7d51cc23 Gitweb: http://git.kernel.org/tip/1e40c2edef2537f87f94d0baf80aeaeb7d51cc23 Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Fri, 19 Jul 2013 20:31:01 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Mon, 22 Jul 2013 10:33:39 +0200
mutex: Fix/document access-once assumption in mutex_can_spin_on_owner() mutex_can_spin_on_owner() is technically broken in that it would in theory allow the compiler to load lock->owner twice, seeing a pointer first time and a NULL pointer the second time. Linus pointed out that a compiler has to be seriously broken to not compile this correctly - but nevertheless this change is correct as it will better document the implementation. Signed-off-by: Peter Zijlstra <pet...@infradead.org> Acked-by: Davidlohr Bueso <davidlohr.bu...@hp.com> Acked-by: Waiman Long <waiman.l...@hp.com> Acked-by: Linus Torvalds <torva...@linux-foundation.org> Acked-by: Thomas Gleixner <t...@linutronix.de> Acked-by: Rik van Riel <r...@redhat.com> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com> Cc: David Howells <dhowe...@redhat.com> Link: http://lkml.kernel.org/r/20130719183101.ga20...@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/mutex.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/mutex.c b/kernel/mutex.c index ff05f4b..7ff48c5 100644 --- a/kernel/mutex.c +++ b/kernel/mutex.c @@ -209,11 +209,13 @@ int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) */ static inline int mutex_can_spin_on_owner(struct mutex *lock) { + struct task_struct *owner; int retval = 1; rcu_read_lock(); - if (lock->owner) - retval = lock->owner->on_cpu; + owner = ACCESS_ONCE(lock->owner); + if (owner) + retval = owner->on_cpu; rcu_read_unlock(); /* * if lock->owner is not set, the mutex owner may have just acquired -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
