[GFS2] kernel panic mounting volume

This patch fixes Red Hat bugzilla bug 450156.

This started with a not-too-improbable mount failure because the
locking protocol was never set back to its proper "lock_dlm" after the
system was rebooted in the middle of a gfs2_fsck.  That left a
(purposely) invalid locking protocol in the superblock, which caused an
error when the file system was mounted the next time.

When there's an error mounting, vfs calls DQUOT_OFF, which calls
vfs_quota_off which calls gfs2_sync_fs.  Next, gfs2_sync_fs calls
gfs2_log_flush passing s_fs_info.  But due to the error, s_fs_info
had been previously set to NULL, and so we have the kernel oops.

My solution in this patch is to test for the NULL value before passing
it.  I tested this patch and it fixes the problem.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/gfs2/ops_super.c b/fs/gfs2/ops_super.c
index 0b7cc920eb89..66907922109f 100644
--- a/fs/gfs2/ops_super.c
+++ b/fs/gfs2/ops_super.c
@@ -155,7 +155,7 @@ static void gfs2_write_super(struct super_block *sb)
 static int gfs2_sync_fs(struct super_block *sb, int wait)
 {
         sb->s_dirt = 0;
-        if (wait)
+        if (wait && sb->s_fs_info)
                 gfs2_log_flush(sb->s_fs_info, NULL);
         return 0;
 }