[Devel] [PATCH RH9 3/4] xfs: terminate perag iteration reliably on agcount

[Kirill Tkhai]

From: Brian Foster <bfoster at redhat.com>

ms commit 8ed004eb9d07

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: 58d43a7e3263 ("xfs: pass perags around in fsmap data dev functions")
Signed-off-by: Brian Foster <bfoster at redhat.com>
Reviewed-by: Dave Chinner <dchinner at redhat.com>
Reviewed-by: Darrick J. Wong <djwong at kernel.org>
Signed-off-by: Darrick J. Wong <djwong at kernel.org>
---
 fs/xfs/libxfs/xfs_ag.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 134e8635dee1..4585ebb3f450 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -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) \