Fix deadlock in journal_create

Hi,
I ran across a deadlock yesterday when trying to do a journal_create
at mount time. The problem is that journal_create does a sync_dev which eventually tries to do a get_super which does:

down_read(&s->s_umount);

The problem arises if I call journal_create from my read_super method in which case get_sb_bdev has already done:

down_write(&s->s_umount);

from alloc_super. Replacing the sync_dev call with an fsync_no_super seems to have fixed the deadlock.

It you want to test this out using ext3 (I have verified it with my own filesystem), simply follow these steps:
1) create an ext2 filesystem on a device
2) mount that new partition and make a "journal file" on it (using dd). get the inode number of that file.
3) unmount it and remount it as an ext3 filesystem using the option:
journal=inode_number where inode number is the inode number of the journal file you just created.
This will get ext3's read_super method to call ext3_create_journal which will hang during a journal_create.

A one line patch is attached. Please let me know what you think.

	--Mark

--
Mark Fasheh
Software Developer, Oracle Corp
[email protected]

@@ -912,7 +912,7 @@ int journal_create(journal_t *journal)
 		__brelse(bh);
 	}
 
-	sync_dev(journal->j_dev);
+	fsync_no_super(journal->j_dev);
 	jbd_debug(1, "JBD: journal cleared.\n");
 
 	/* OK, fill in the initial static fields in the new superblock */

Hi,

Looks OK to me.

--Stephen