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Re: [PATCH] xfs: Keep sb_bad_features2 consistent with sb_features2

To: Jan Kara <jack@xxxxxxx>
Subject: Re: [PATCH] xfs: Keep sb_bad_features2 consistent with sb_features2
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 24 Dec 2014 09:17:46 +1100
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20141218095919.GA13705@xxxxxxxxxxxxx>
References: <1418848046-11265-1-git-send-email-jack@xxxxxxx> <20141217212255.GZ24183@dastard> <20141218095919.GA13705@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Dec 18, 2014 at 10:59:19AM +0100, Jan Kara wrote:
> On Thu 18-12-14 08:22:55, Dave Chinner wrote:
> > On Wed, Dec 17, 2014 at 09:27:26PM +0100, Jan Kara wrote:
> > > Currently when we modify sb_features2, we store the same value also in
> > > sb_bad_features2. However in most places we forget to mark field
> > > sb_bad_features2 for logging and thus it can happen that a change to it
> > > is lost. This results in an inconsistent sb_features2 and
> > > sb_bad_features2 fields e.g. after xfstests test xfs/187.
> > > 
> > > Fix the problem by changing XFS_SB_FEATURES2 to actually mean both
> > > sb_features2 and sb_bad_features2 fields since this is always what we
> > > want to log. This isn't ideal because the fact that XFS_SB_FEATURES2
> > > means two fields could cause some problem in future however the code is
> > > hopefully less error prone that it is now.
> > 
> > Actually, I have patches that fix this differently that I'm planning
> > to push for the 3.20 cycle.  They get rid of the "update random SB
> > fields" problem altogether simply by logging and updating the entire
> > SB every time.
> > 
> > http://oss.sgi.com/archives/xfs/2014-09/msg00448.html
>   OK, thanks for info.

FWIW, I'll pull the fixes you have posted and rebase the rework I
have on top of them. That way we have fixes that can be backported
easily without pulling the entire rework in the commit history.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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