diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2013-07-19 20:31:01 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2013-07-22 10:33:39 +0200 |
| commit | 1e40c2edef2537f87f94d0baf80aeaeb7d51cc23 (patch) | |
| tree | 3692ad447e3242ab2042edfd09d24107d5166652 /kernel/mutex.c | |
| parent | c4be9cb4f19cbd534a6c4c334cd48d8bb483e17a (diff) | |
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 <peterz@infradead.org>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Acked-by: Waiman Long <Waiman.Long@hp.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Link: http://lkml.kernel.org/r/20130719183101.GA20909@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/mutex.c')
| -rw-r--r-- | kernel/mutex.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/mutex.c b/kernel/mutex.c index ff05f4bd86eb..7ff48c55a98b 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 |