[xfs-masters] [PATCH] update sb->s_frozen when freezing read-only mounted device, too

[Akinobu Mita <akinobu.mita@xxxxxxxxx>]

freeze_bdev() with the device which is mounted as read only
does not change sb->s_frozen from SB_UNFROZEN to SB_FREEZE_TRANS.

Because of this behavior, xfs_freeze can break read-only XFS filesystem.

Because xfs_thaw does nothing for the filesystem whose sb->s_frozen is
SB_UNFROZEN. So freezed readonly XFS filesystem will never be unfreezed.
Then we cannot do any unmount/remount operations for that filesystem.

This patch updates sb->s_frozen when freeze_bdev() is called for read-only
mounted device, too.

Cc:  Tim Shimmin <xfs-masters@xxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>

---
 fs/buffer.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

Index: 2.6-git/fs/buffer.c
===================================================================
--- 2.6-git.orig/fs/buffer.c
+++ 2.6-git/fs/buffer.c
@@ -190,19 +190,22 @@ struct super_block *freeze_bdev(struct b
 
        down(&bdev->bd_mount_sem);
        sb = get_super(bdev);
-       if (sb && !(sb->s_flags & MS_RDONLY)) {
+       if (sb) {
                sb->s_frozen = SB_FREEZE_WRITE;
                smp_wmb();
 
-               __fsync_super(sb);
+               if (!(sb->s_flags & MS_RDONLY))
+                       __fsync_super(sb);
 
                sb->s_frozen = SB_FREEZE_TRANS;
                smp_wmb();
 
-               sync_blockdev(sb->s_bdev);
+               if (!(sb->s_flags & MS_RDONLY)) {
+                       sync_blockdev(sb->s_bdev);
 
-               if (sb->s_op->write_super_lockfs)
-                       sb->s_op->write_super_lockfs(sb);
+                       if (sb->s_op->write_super_lockfs)
+                               sb->s_op->write_super_lockfs(sb);
+               }
        }
 
        sync_blockdev(bdev);