Messages in this thread | | | Subject | Re: [PATCH] mutex: Fix mutex_can_spin_on_owner | From | Davidlohr Bueso <> | Date | Fri, 19 Jul 2013 11:36:29 -0700 |
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On Fri, 2013-07-19 at 20:31 +0200, Peter Zijlstra wrote: > mutex_can_spin_on_owner() is broken in that it would allow the compiler > to load lock->owner twice, seeing a pointer first time and a MULL > pointer the second time. > > Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Yep, I remember this from the rwsem optimistic spinning thread.
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
> --- > 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
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