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>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e046eba..282a270 100644 (file)
--- 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. */
@@ -3608,7 +3608,7 @@ 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);
        }