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xfs: terminate perag iteration reliably on agcount 

The for_each_perag_from() iteration macro relies on sb_agcount to
process every perag currently within EOFS from a given starting
point. It's perfectly valid to have perag structures beyond
sb_agcount, however, such as if a growfs is in progress. If a perag
loop happens to race with growfs in this manner, it will actually
attempt to process the post-EOFS perag where ->pag_agno ==
sb_agcount. This is reproduced by xfs/104 and manifests as the
following assert failure in superblock write verifier context:

 XFS: Assertion failed: agno < mp->m_sb.sb_agcount, file: fs/xfs/libxfs/xfs_types.c, line: 22

Update the corresponding macro to only process perags that are
within the current sb_agcount.

Fixes: 58d43a7e32 ("xfs: pass perags around in fsmap data dev functions")
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
This commit is contained in:
Brian Foster 2021-10-14 12:56:09 -07:00 committed by Darrick J. Wong
parent f1788b5e5e
commit 8ed004eb9d
1 changed files with 1 additions and 1 deletions
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2
fs/xfs/libxfs/xfs_ag.h
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@ -142,7 +142,7 @@ xfs_perag_next(
(pag) = xfs_perag_next((pag), &(agno)))
#define for_each_perag_from(mp, agno, pag) \
for_each_perag_range((mp), (agno), (mp)->m_sb.sb_agcount, (pag))
for_each_perag_range((mp), (agno), (mp)->m_sb.sb_agcount - 1, (pag))
#define for_each_perag(mp, agno, pag) \