From: Dave Chinner dchinner@redhat.com
commit c9fbd7bbc23dbdd73364be4d045e5d3612cf6e82 upstream.
We recently had an oops reported on a 4.14 kernel in xfs_reclaim_inodes_count() where sb->s_fs_info pointed to garbage and so the m_perag_tree lookup walked into lala land.
Essentially, the machine was under memory pressure when the mount was being run, xfs_fs_fill_super() failed after allocating the xfs_mount and attaching it to sb->s_fs_info. It then cleaned up and freed the xfs_mount, but the sb->s_fs_info field still pointed to the freed memory. Hence when the superblock shrinker then ran it fell off the bad pointer.
With the superblock shrinker problem fixed at teh VFS level, this stale s_fs_info pointer is still a problem - we use it unconditionally in ->put_super when the superblock is being torn down, and hence we can still trip over it after a ->fill_super call failure. Hence we need to clear s_fs_info if xfs-fs_fill_super() fails, and we need to check if it's valid in the places it can potentially be dereferenced after a ->fill_super failure.
Signed-Off-By: Dave Chinner dchinner@redhat.com Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Ajay Kaher akaher@vmware.com --- fs/xfs/xfs_super.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c index ef64a1e..ff3f581 100644 --- a/fs/xfs/xfs_super.c +++ b/fs/xfs/xfs_super.c @@ -1572,6 +1572,7 @@ xfs_fs_fill_super( out_close_devices: xfs_close_devices(mp); out_free_fsname: + sb->s_fs_info = NULL; xfs_free_fsname(mp); kfree(mp); out: @@ -1589,6 +1590,10 @@ xfs_fs_put_super( { struct xfs_mount *mp = XFS_M(sb);
+ /* if ->fill_super failed, we have no mount to tear down */ + if (!sb->s_fs_info) + return; + xfs_notice(mp, "Unmounting Filesystem"); xfs_filestream_unmount(mp); xfs_unmountfs(mp); @@ -1598,6 +1603,8 @@ xfs_fs_put_super( xfs_destroy_percpu_counters(mp); xfs_destroy_mount_workqueues(mp); xfs_close_devices(mp); + + sb->s_fs_info = NULL; xfs_free_fsname(mp); kfree(mp); } @@ -1617,6 +1624,9 @@ xfs_fs_nr_cached_objects( struct super_block *sb, struct shrink_control *sc) { + /* Paranoia: catch incorrect calls during mount setup or teardown */ + if (WARN_ON_ONCE(!sb->s_fs_info)) + return 0; return xfs_reclaim_inodes_count(XFS_M(sb)); }