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 <pet...@infradead.org>
Yep, I remember this from the rwsem optimistic spinning thread.
Acked-by: Davidlohr Bueso <davidlohr.bu...@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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