From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752894AbbHMOAz (ORCPT <rfc822;w@1wt.eu>);
	Thu, 13 Aug 2015 10:00:55 -0400
Received: from mx1.redhat.com ([209.132.183.28]:60918 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752249AbbHMOAy (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Thu, 13 Aug 2015 10:00:54 -0400
Date: Thu, 13 Aug 2015 15:58:38 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Jan Kara <jack@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Dave Chinner <david@fromorbit.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 9/8] don't fool lockdep in freeze_super() and
	thaw_super() paths
Message-ID: <20150813135838.GA17414@redhat.com>
References: <20150811170343.GA26881@redhat.com> <20150812131138.GA7462@redhat.com> <20150813110155.GI26599@quack.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150813110155.GI26599@quack.suse.cz>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 08/13, Jan Kara wrote:
>
> On Wed 12-08-15 15:11:38, Oleg Nesterov wrote:
> > On 08/11, Oleg Nesterov wrote:
> > >
> > > The only essential change is that I dropped the lockdep improvements
> > > as we discussed. This means that 8/8 was changed a bit, and I decided
> > > to add the new documentation patch, see 3/8.
> >
> > Update: The recent
> >
> > 	[PATCH 0/2] xfs: kill lockdep false positives from readdir
> >
> > changes from Dave fixed the problems ILOCK false-positives. So we can
> > add the additional patch which (modulo comments) just turns v2 back into
> > v1.
> >
> > Dave, Jan, you seem to agree with these patches. How should we route
> > this all?
>
> Regarding the routing, ideally Al Viro should take these as a VFS
> maintainer.

OK. I'll send v3.

But to remind, this particular patch depends on Dave's fixes, so I will
send it later.

And I forgot to mention that I have another patch which removes the
trylock hack from __sb_start_write() as Dave suggested, it passed the
tests. But again, I'd really like to send it separately so that it can
be reverted in (unlikely) case something else does recursive read_lock().

> > Subject: [PATCH v2 9/8] don't fool lockdep in freeze_super() and thaw_super() paths
> >
> > sb_wait_write()->percpu_rwsem_release() fools lockdep to avoid the
> > false-positives. Now that xfs was fixed by Dave we can remove it and
> > change freeze_super() and thaw_super() to run with s_writers.rw_sem
> > locks held; we add two trivial helpers for that, sb_freeze_release()
> > and sb_freeze_acquire().
> >
> > While at it, kill the outdated part of the comment above sb_wait_write.
> >
> > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
>
> The patch looks good. Just one nit:
>
> > +	for (level = SB_FREEZE_LEVELS; --level >= 0; )
> > +		percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
>
> It is more common (and to me more readable) to have the loop written as:
>
> for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
>
> I agree what you do is shorter but IMHO it's just an unnecessary
> obfuscation :)

Agreed, will fix.

Oleg.