Re: [PATCH] xfs: update superblock counters correctly for !lazysbcount

[Gao Xiang <hsiangkao@redhat.com>]

Hi Darrick,

On Mon, Apr 26, 2021 at 08:07:15PM -0700, Darrick J. Wong wrote:
> On Tue, Apr 27, 2021 at 09:12:01AM +0800, Gao Xiang wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > Keep the mount superblock counters up to date for !lazysbcount
> > filesystems so that when we log the superblock they do not need
> > updating in any way because they are already correct.
> > 
> > It's found by what Zorro reported:
> > 1. mkfs.xfs -f -l lazy-count=0 -m crc=0 $dev
> > 2. mount $dev $mnt
> > 3. fsstress -d $mnt -p 100 -n 1000 (maybe need more or less io load)
> > 4. umount $mnt
> > 5. xfs_repair -n $dev
> > and I've seen no problem with this patch.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > Reported-by: Zorro Lang <zlang@redhat.com>
> > Reviewed-by: Gao Xiang <hsiangkao@redhat.com>
> > Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> > ---
> > 
> > As per discussion earilier [1], use the way Dave suggested instead.
> > Also update the line to
> > 	mp->m_sb.sb_fdblocks += tp->t_fdblocks_delta + tp->t_res_fdblocks_delta;
> > so it can fix the case above.
> > 
> > with XFS debug off, xfstests auto testcases fail on my loop-device-based
> > testbed with this patch and Darrick's [2]:
> > 
> > generic/095 generic/300 generic/600 generic/607 xfs/073 xfs/148 xfs/273
> > xfs/293 xfs/491 xfs/492 xfs/495 xfs/503 xfs/505 xfs/506 xfs/514 xfs/515
> 
> Hmm, with the following four patches applied:
> 
> https://lore.kernel.org/linux-xfs/20210427000204.GC3122264@magnolia/T/#u
> https://lore.kernel.org/linux-xfs/20210425225110.GD63242@dread.disaster.area/T/#t
> https://lore.kernel.org/linux-xfs/20210427011201.4175506-1-hsiangkao@redhat.com/T/#u
> https://lore.kernel.org/linux-xfs/20210427030232.GE3122264@magnolia/T/#u
> 
> I /think/ all the obvious problems with !lazysbcount filesystems are
> fixed.  The exceptions AFAICT are xfs/491 and xfs/492, which fuzz the
> summary counters; we'll deal with those later.

Yeah, I agree, some failure above may be due to my environment setting
and seems always failure (I use loop device). Also, it'd be better to
reconfirm on the Zorro's side.

I noticed xfs/491 and xfs/492, I think !lazysbcount filesystems just
blindly trust sb counters even with dirty log. So I think we might
just skip the testcase and that would be fine? (Or recalc with obvious
corrupted values...)

Thanks,
Gao Xiang

> 
> --D
> 
> > 
> > MKFS_OPTIONS="-mcrc=0 -llazy-count=0"
> > 
> > and these testcases above still fail without these patches or with
> > XFS debug on, so I've seen no regression due to this patch.
> > 
> > [1] https://lore.kernel.org/r/20210422030102.GA63242@dread.disaster.area/
> > [2] https://lore.kernel.org/r/20210425154634.GZ3122264@magnolia/
> > 
> >  fs/xfs/libxfs/xfs_sb.c | 16 +++++++++++++---
> >  fs/xfs/xfs_trans.c     |  3 +++
> >  2 files changed, 16 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> > index 60e6d255e5e2..dfbbcbd448c1 100644
> > --- a/fs/xfs/libxfs/xfs_sb.c
> > +++ b/fs/xfs/libxfs/xfs_sb.c
> > @@ -926,9 +926,19 @@ xfs_log_sb(
> >  	struct xfs_mount	*mp = tp->t_mountp;
> >  	struct xfs_buf		*bp = xfs_trans_getsb(tp);
> >  
> > -	mp->m_sb.sb_icount = percpu_counter_sum(&mp->m_icount);
> > -	mp->m_sb.sb_ifree = percpu_counter_sum(&mp->m_ifree);
> > -	mp->m_sb.sb_fdblocks = percpu_counter_sum(&mp->m_fdblocks);
> > +	/*
> > +	 * Lazy sb counters don't update the in-core superblock so do that now.
> > +	 * If this is at unmount, the counters will be exactly correct, but at
> > +	 * any other time they will only be ballpark correct because of
> > +	 * reservations that have been taken out percpu counters. If we have an
> > +	 * unclean shutdown, this will be corrected by log recovery rebuilding
> > +	 * the counters from the AGF block counts.
> > +	 */
> > +	if (xfs_sb_version_haslazysbcount(&mp->m_sb)) {
> > +		mp->m_sb.sb_icount = percpu_counter_sum(&mp->m_icount);
> > +		mp->m_sb.sb_ifree = percpu_counter_sum(&mp->m_ifree);
> > +		mp->m_sb.sb_fdblocks = percpu_counter_sum(&mp->m_fdblocks);
> > +	}
> >  
> >  	xfs_sb_to_disk(bp->b_addr, &mp->m_sb);
> >  	xfs_trans_buf_set_type(tp, bp, XFS_BLFT_SB_BUF);
> > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > index bcc978011869..1e37aa8eca5a 100644
> > --- a/fs/xfs/xfs_trans.c
> > +++ b/fs/xfs/xfs_trans.c
> > @@ -629,6 +629,9 @@ xfs_trans_unreserve_and_mod_sb(
> >  
> >  	/* apply remaining deltas */
> >  	spin_lock(&mp->m_sb_lock);
> > +	mp->m_sb.sb_fdblocks += tp->t_fdblocks_delta + tp->t_res_fdblocks_delta;
> > +	mp->m_sb.sb_icount += idelta;
> > +	mp->m_sb.sb_ifree += ifreedelta;
> >  	mp->m_sb.sb_frextents += rtxdelta;
> >  	mp->m_sb.sb_dblocks += tp->t_dblocks_delta;
> >  	mp->m_sb.sb_agcount += tp->t_agcount_delta;
> > -- 
> > 2.27.0
> > 
>