On Fri, 2016-05-20 at 16:27 -0400, Waiman Long wrote:
> On 05/19/2016 06:23 PM, Jason Low wrote:
> > The mutex owner can get read and written to without the wait_lock.
> > Use WRITE_ONCE when setting and clearing the owner field in order
> > to avoid optimizations such as store tearing. This avoids
> > situations where the owner field gets written to with multiple
> > stores and another thread could concurrently read and use a
> > partially written owner value.
> >
> > Signed-off-by: Jason Low<jason.l...@hpe.com>
> > ---
> > kernel/locking/mutex.h | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
> > index 5cda397..469b61e 100644
> > --- a/kernel/locking/mutex.h
> > +++ b/kernel/locking/mutex.h
> > @@ -17,14 +17,20 @@
> > __list_del((waiter)->list.prev, (waiter)->list.next)
> >
> > #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
> > +/*
> > + * The mutex owner can get read and written to locklessly.
> > + * We should use WRITE_ONCE() when writing the owner value to
> > + * avoid store tearing, otherwise, a thread could potentially
> > + * read a partially written and incomplete owner value.
> > + */
> > static inline void mutex_set_owner(struct mutex *lock)
> > {
> > - lock->owner = current;
> > + WRITE_ONCE(lock->owner, current);
> > }
> >
> > static inline void mutex_clear_owner(struct mutex *lock)
> > {
> > - lock->owner = NULL;
> > + WRITE_ONCE(lock->owner, NULL);
> > }
> > #else
> > static inline void mutex_set_owner(struct mutex *lock)
>
> I think mutex-debug.h also needs similar changes for completeness.
Good point, I will add the changes to those functions in the debug case
to this patch.
Thanks,
Jason
