On Thu, Aug 02, 2012 at 08:11:58AM -0400, Josef Bacik wrote:
> On Thu, Aug 02, 2012 at 04:46:44AM -0600, Liu Bo wrote:
> > On 08/02/2012 04:25 AM, Josef Bacik wrote:
> > > We need an smb_mb() before waitqueue_active to avoid missing wakeups.
> > > Before Mitch was hitting a deadlock between the ordered flushers and the
> > > transaction commit because the ordered flushers were waiting for more refs
> > > and were never woken up, so those smp_mb()'s are the most important.
> > > Everything else I added for correctness sake and to avoid getting bitten
> > > by
> > > this again somewhere else. Thanks,
> >
> > I'll appreciate a lot if you can add some comments for each memory
> > barrier, because not everyone knows why it is used here and there. :)
>
> I'm not going to add comments to all those places, you need a memory barrier
> in
> places you don't have an implicit barrier before you do waitqueue_active
> because
> you could miss somebody being added to the waitqueue, it's just basic
> correctness. Thanks,
This asks for a helper:
+ smp_mb();
+ if (waitqueue_active(&fs_info->async_submit_wait))
+ wake_up(&fs_info->async_submit_wait);
->
void wake_up_if_active(wait) {
/*
* the comment
*/
smp_mb();
if(waitqueue_active(wait)
wake_up(wait);
}
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