Messages in this thread | | | Date | Wed, 15 Jan 2014 08:48:44 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC 1/3] mutex: In mutex_can_spin_on_owner(), return false if task need_resched() |
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On Wed, Jan 15, 2014 at 08:44:20AM +0100, Peter Zijlstra wrote: > On Tue, Jan 14, 2014 at 04:33:08PM -0800, Jason Low wrote: > > The mutex_can_spin_on_owner() function should also return false if the > > task needs to be rescheduled. > > > > While I was staring at mutex_can_spin_on_owner(); don't we need this? > > kernel/locking/mutex.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index 4dd6e4c219de..480d2f437964 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -214,8 +214,10 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock) > > rcu_read_lock(); > owner = ACCESS_ONCE(lock->owner); > - if (owner) > + if (owner) {
That is, its an unmatched barrier, as mutex_set_owner() doesn't include a barrier, and I don't think i needs to; but on alpha we still need this read barrier to ensure we do not mess up this related load afaik.
Paul? can you explain an unpaired read_barrier_depends?
> + smp_read_barrier_depends(); > retval = owner->on_cpu; > + } > rcu_read_unlock(); > /* > * if lock->owner is not set, the mutex owner may have just acquired
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