quota: Fix deadlock with suspend and quotas
authorJan Kara <jack@suse.cz>
Fri, 10 Feb 2012 10:03:01 +0000 (11:03 +0100)
committerAl Viro <viro@zeniv.linux.org.uk>
Tue, 14 Feb 2012 01:45:39 +0000 (20:45 -0500)
commitdcdbed853d9fbb0547b781ba676049b87f54129a
tree6f8f2382e7aef99ec21ae9c4dfbfe18e47d4626c
parent6b6dc836a195e077e76977b6c020a73de411b46d
quota: Fix deadlock with suspend and quotas

This script causes a kernel deadlock:
set -e
DEVICE=/dev/vg1/linear
lvchange -ay $DEVICE
mkfs.ext3 $DEVICE
mount -t ext3 -o usrquota,grpquota $DEVICE /mnt/test
quotacheck -gu /mnt/test
umount /mnt/test
mount -t ext3 -o usrquota,grpquota $DEVICE /mnt/test
quotaon /mnt/test
dmsetup suspend $DEVICE
setquota -u root 1 2 3 4 /mnt/test &
sleep 1
dmsetup resume $DEVICE

setquota acquired semaphore s_umount for read and then tried to perform a
transaction (and waits because the device is suspended).  dmsetup resume tries
to acquire s_umount for write before resuming the device (and waits for
setquota).

Fix the deadlock by grabbing a thawed superblock for quota commands which need
it.

Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
fs/quota/quota.c