[Devel] [PATCH RHEL9 COMMIT] ms/xfs: terminate perag iteration reliably on agcount

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.vz9.1.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh9-5.14.0-4.vz9.10.33
------>
commit e6b8d46b2badb0179ff506c00c20d3c339feb888
Author: Brian Foster <bfoster at redhat.com>
Date:   Tue Dec 7 18:14:46 2021 +0300

    ms/xfs: terminate perag iteration reliably on agcount
    
    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>
    
    Feature: fix ms/xfs
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 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) \