On Tue, Nov 03, 2015 at 06:59:58PM +0100, Oleg Nesterov wrote: > > - raw_spin_unlock_wait(&task->pi_lock); > > - smp_mb(); > > + smp_cond_acquire(!raw_spin_is_locked(&task->pi_lock)); > > Unfortunately this doesn't look exactly right... > > spin_unlock_wait() is not equal to "while (locked) relax", the latter > is live-lockable or at least sub-optimal: we do not really need to spin > until we observe !spin_is_locked(), we only need to synchronize with the > current owner of this lock. Once it drops the lock we can proceed, we > do not care if another thread takes the same lock right after that.
Ah indeed. And while every use of spin_unlock_wait() has 'interesting' barriers associated, they all seem different. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/