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Re: [PATCH 1/6] xfs: rework dquot CRCs

To: Dave Chinner <dchinner@xxxxxxxxxx>, Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH 1/6] xfs: rework dquot CRCs
From: Ben Myers <bpm@xxxxxxx>
Date: Tue, 4 Jun 2013 17:07:12 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130604214612.GL20932@xxxxxxx>
References: <1370237332-24757-1-git-send-email-david@xxxxxxxxxxxxx> <1370237332-24757-2-git-send-email-david@xxxxxxxxxxxxx> <51ACDDF9.1040202@xxxxxxxxxx> <20130604214612.GL20932@xxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Tue, Jun 04, 2013 at 04:46:12PM -0500, Ben Myers wrote:
> On Mon, Jun 03, 2013 at 02:18:33PM -0400, Brian Foster wrote:
> > On 06/03/2013 01:28 AM, Dave Chinner wrote:
> > > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > > 
> > > Calculating dquot CRCs when the backing buffer is written back just
> > > doesn't work reliably. There are several places which manipulate
> > > dquots directly in the buffers, and they don't calculate CRCs
> > > appropriately, nor do they always set the buffer up to calculate
> > > CRCs appropriately.
> > > 
> > > Firstly, if we log a dquot buffer (e.g. during allocation) it gets
> > > logged without valid CRC, and so on recovery we end up with a dquot
> > > that is not valid.
> > > 
> > > Secondly, if we recover/repair a dquot, we don't have a verifier
> > > attached to the buffer and hence CRCs arenot calculate don the way
> > > down to disk.
> > > 
> > > Thirdly, calculating the CRC after we've changed the contents means
> > > that if we re-read the dquot from the buffer, we cannot verify the
> > > contents of the dquot are valid, as the CRC is invalid.
> > > 
> > > So, to avoid all the dquot CRC errors that are being detected by the
> > > read verifier, change to using the same model as for inodes. that
> > > is, dquot CRCs are calculated and written to the backing buffer at
> > > the time the dquot is flushed to the backing buffer. If we modify
> > > the dquuot directly in the backing buffer, calculate the CRC
> > > immediately after the modification is complete. Hence the dquot in
> > > the on-disk buffer should always have a valid CRC.
> > > 
> > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > 
> > Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> > 
> > > ---
> > >  fs/xfs/xfs_dquot.c       |   37 ++++++++++++++++---------------------
> > >  fs/xfs/xfs_log_recover.c |   10 ++++++++++
> > >  fs/xfs/xfs_qm.c          |   40 ++++++++++++++++++++++++++++++----------
> > >  fs/xfs/xfs_quota.h       |    2 ++
> > >  4 files changed, 58 insertions(+), 31 deletions(-)
> > > 
> > > diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
> > > index a41f8bf..044e97a 100644
> > > --- a/fs/xfs/xfs_dquot.c
> > > +++ b/fs/xfs/xfs_dquot.c
> > > @@ -249,8 +249,11 @@ xfs_qm_init_dquot_blk(
> > >           d->dd_diskdq.d_version = XFS_DQUOT_VERSION;
> > >           d->dd_diskdq.d_id = cpu_to_be32(curid);
> > >           d->dd_diskdq.d_flags = type;
> > > -         if (xfs_sb_version_hascrc(&mp->m_sb))
> > > +         if (xfs_sb_version_hascrc(&mp->m_sb)) {
> > >                   uuid_copy(&d->dd_uuid, &mp->m_sb.sb_uuid);
> > > +                 xfs_update_cksum((char *)d, sizeof(struct xfs_dqblk),
> > > +                                  XFS_DQUOT_CRC_OFF);
> > > +         }
> > >   }
> > >  
> > >   xfs_trans_dquot_buf(tp, bp,
> 
> Huh.  Looks like this buffer will not be recovered.  See
> xlog_recover_do_reg_buffer... I think he'll be skipped in recovery.  Goto 
> next.
> 
> That's not an issue with this patch though.
>
> Reviewed-by: Ben Myers <bpm@xxxxxxx>

No Ben that is only on error.  ;)

Applied.

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