[PATCH] ext4: fix freeze deadlock under IO

Commit 6b0310fbf087ad6 caused a regression resulting in deadlocks

when freezing a filesystem which had active IO; the vfs_check_frozen

level (SB_FREEZE_WRITE) did not let the freeze-related IO syncing

through.  Duh.

Changing the test to FREEZE_TRANS should let the normal freeze

syncing get through the fs, but still block any transactions from

starting once the fs is completely frozen.

I tested this by running fsstress in the background while periodically

snapshotting the fs and running fsck on the result.  I ran into

occasional deadlocks, but different ones.  I think this is a

fine fix for the problem at hand, and the other deadlocky things

will need more investigation.

Reported-by: Phillip Susi <psusi@cfl.rr.com>

Signed-off-by: Eric Sandeen <sandeen@redhat.com>

---

diff --git a/fs/ext4/super.c b/fs/ext4/super.c

index 4e8983a..a45ced9 100644

--- a/fs/ext4/super.c

+++ b/fs/ext4/super.c

@@ -241,7 +241,7 @@ handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks)

 	if (sb->s_flags & MS_RDONLY)

 		return ERR_PTR(-EROFS);

-	vfs_check_frozen(sb, SB_FREEZE_WRITE);

+	vfs_check_frozen(sb, SB_FREEZE_TRANS);

 	/* Special case here: if the journal has aborted behind our

 	 * backs (eg. EIO in the commit thread), then we still need to

 	 * take the FS itself readonly cleanly. */

@@ -3491,7 +3491,7 @@ int ext4_force_commit(struct super_block *sb)

 	journal = EXT4_SB(sb)->s_journal;

 	if (journal) {

-		vfs_check_frozen(sb, SB_FREEZE_WRITE);

+		vfs_check_frozen(sb, SB_FREEZE_TRANS);

 		ret = ext4_journal_force_commit(journal);

 	}