When an ext3 partition is mounted and then quickly unmounted, the journal
thread never gets around to checking the JFS_UNMOUNT flag (it immediately
goes into a loop waiting for a new sequence number), causing the umount
process to hang in journal_kill_thread().

The problem can be easily reproduced by roughly the following steps:

	dd if=/dev/zero of=/tmp/qf bs=1024k count=10
	yes | mke2fs -j /tmp/qf
	losetup /dev/loop0 /tmp/qf
	mkdir /mnt/qf
	mount -t ext3 /dev/loop0 /mnt/qf ; umount /mnt/qf

The patch below moves the check for JFS_UNMOUNT to the beginning of the
journal thread loop, thereby preventing this race condition.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>