[PATCH] xfs: don't use in-core per-cpu fdblocks for !lazysbcount

[Gao Xiang <hsiangkao@redhat.com>]

There are many paths which could trigger xfs_log_sb(), e.g.
  xfs_bmap_add_attrfork()
    -> xfs_log_sb()
, which overrided on-disk fdblocks by in-core per-CPU fdblocks.

However, for !lazysbcount cases, on-disk fdblocks is actually updated
by xfs_trans_apply_sb_deltas(), and generally it isn't equal to
in-core fdblocks due to xfs_reserve_block() or whatever, see the
comment in xfs_unmountfs().

It could be observed by the following steps reported by Zorro [1]:

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

yet due to commit f46e5a174655("xfs: fold sbcount quiesce logging
into log covering"), xfs_sync_sb() will be triggered even !lazysbcount
but xfs_log_need_covered() case when xfs_unmountfs(), so hard to
reproduce on kernel 5.12+.

After this patch, I've seen no strange so far on older kernels
for the testcase above without lazysbcount.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1949515

Reported-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 fs/xfs/libxfs/xfs_sb.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index 60e6d255e5e2..423dada3f64c 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -928,7 +928,13 @@ xfs_log_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);
+	if (!xfs_sb_version_haslazysbcount(&mp->m_sb)) {
+		struct xfs_dsb	*dsb = bp->b_addr;
+
+		mp->m_sb.sb_fdblocks = be64_to_cpu(dsb->sb_fdblocks);
+	} else {
+		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);
-- 
2.27.0