On Sat 18-07-15 08:40:15, Dave Chinner wrote:
> On Fri, Jul 17, 2015 at 07:31:17PM +0200, Oleg Nesterov wrote:
> > On 07/17, Dave Chinner wrote:
> > >
> > > On Thu, Jul 16, 2015 at 07:32:56PM +0200, Oleg Nesterov wrote:
> > > >
> > > > #ifdef CONFIG_LOCKDEP
> > > > /*
> > > > * We want lockdep to tell us about possible deadlocks
> > > > with freezing but
> > > > * it's it bit tricky to properly instrument it.
> > > > Getting a freeze protection
> > > > * works as getting a read lock but there are subtle
> > > > problems. XFS for example
> > > > * gets freeze protection on internal level twice in
> > > > some cases, which is OK
> > >
> > > Sorry, I've missed something here - where is XFS nesting
> > > sb_start_intwrite() calls?
> >
> > Heh ;) I too tried to understand thi but failed. I was not surprized,
> > I know nothing about fs/.
> >
> > Dave, I didn't write this comment. Please look at acquire_freeze_lock().
> > If we can remove this logic - great! but this needs a separate change.
>
> Oh, I think I know what it was - when we duplicate a transaction for
> a rolling commit, we do it before committing the current transaction
> is committed. I *think* that used to take a second freeze reference,
> which only existed until the first transaction was committed. We do
> things a bit differently now - we hold a state flag on the
> transaction to indicate it needs to release the freeze reference
> when it is freed and we pass it to the new transaction so that the
> first transaction commit doesn't release it.
>
> So, yes, it may well be a stale comment now.
Yeah, as far as I remember this was the reason why I added the comment. So
Oleg, feel free to remove the special code and run xfstests with XFS and
lockdep enabled to verify there are really no issues. Thanks!
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
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