[dm-devel] [PATCH] deadlock with suspend and quotas

[Mikulas Patocka]

This script causes a kernel deadlock:
#!/bin/sh
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).

Here are stacktraces:
setquota:
[   67.524456]  [<ffffffff810aa84e>] ? get_page_from_freelist+0x31e/0x790
[   67.524529]  [<ffffffffa0250265>] ? start_this_handle.isra.9+0x265/0x3b0 [jbd]
[   67.524604]  [<ffffffff8105bc00>] ? add_wait_queue+0x60/0x60
[   67.524675]  [<ffffffffa02505a1>] ? journal_start+0xc1/0x100 [jbd]
[   67.524742]  [<ffffffff810e62d6>] ? kmem_cache_alloc+0xf6/0x1b0
[   67.524808]  [<ffffffffa028018d>] ? ext3_acquire_dquot+0x3d/0x80 [ext3]
[   67.524872]  [<ffffffff81143749>] ? dqget+0x359/0x3b0
[   67.524916]  [<ffffffff81143ad4>] ? dquot_get_dqblk+0x14/0x1b0
[   67.524985]  [<ffffffff81147c34>] ? quota_getquota+0x24/0xd0
[   67.525048]  [<ffffffff810ff3db>] ? do_path_lookup+0x2b/0x90
[   67.525082]  [<ffffffff810ff8cd>] ? kern_path+0x1d/0x40
[   67.525134]  [<ffffffff81148311>] ? do_quotactl+0x421/0x540
[   67.525191]  [<ffffffff811073f0>] ? dput+0x20/0x230
[   67.525234]  [<ffffffff81148507>] ? sys_quotactl+0xd7/0x1a0
[   67.525304]  [<ffffffff8130a03b>] ? system_call_fastpath+0x16/0x1b

dmsetup resume:
[   67.525887]  [<ffffffffa0238280>] ? dev_wait+0xc0/0xc0 [dm_mod]
[   67.525948]  [<ffffffff81309225>] ? rwsem_down_failed_common+0xc5/0x160
[   67.526013]  [<ffffffff81198a43>] ? call_rwsem_down_write_failed+0x13/0x20
[   67.526058]  [<ffffffff81308adc>] ? down_write+0x1c/0x1d
[   67.526103]  [<ffffffff810f3a91>] ? thaw_super+0x21/0xc0
[   67.526166]  [<ffffffff81124d4d>] ? thaw_bdev+0x6d/0x90
[   67.526223]  [<ffffffff8105583e>] ? queue_work+0x4e/0x60
[   67.526269]  [<ffffffffa0230e63>] ? unlock_fs+0x23/0x40 [dm_mod]
[   67.526341]  [<ffffffffa02336d0>] ? dm_resume+0xb0/0xd0 [dm_mod]
[   67.526388]  [<ffffffffa0238420>] ? dev_suspend+0x1a0/0x230 [dm_mod]
[   67.526441]  [<ffffffffa0238a59>] ? ctl_ioctl+0x159/0x2a0 [dm_mod]
[   67.526510]  [<ffffffff8116c4ee>] ? ipc_addid+0x4e/0xd0
[   67.526555]  [<ffffffffa0238bae>] ? dm_ctl_ioctl+0xe/0x20 [dm_mod]
[   67.526620]  [<ffffffff811025de>] ? do_vfs_ioctl+0x8e/0x4e0
[   67.526670]  [<ffffffff811073f0>] ? dput+0x20/0x230
[   67.526737]  [<ffffffff810f3112>] ? fput+0x162/0x220
[   67.526783]  [<ffffffff81102a79>] ? sys_ioctl+0x49/0x90
[   67.526838]  [<ffffffff8130a03b>] ? system_call_fastpath+0x16/0x1b

The following patch fixes the deadlock. When the quota subsystem takes s_umount,
it checks if the filesystem is frozen. If it is, we drop s_umount, wait for
the filesystem to resume and retry.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
CC: stable at kernel.org

---
 fs/quota/quota.c   |   12 ++++++++++++
 include/linux/fs.h |    1 +
 2 files changed, 13 insertions(+)

Index: linux-3.1-fast/fs/quota/quota.c
===================================================================
--- linux-3.1-fast.orig/fs/quota/quota.c	2011-11-25 20:19:14.000000000 +0100
+++ linux-3.1-fast/fs/quota/quota.c	2011-11-25 21:12:32.000000000 +0100
@@ -310,7 +310,19 @@ static struct super_block *quotactl_bloc
 	putname(tmp);
 	if (IS_ERR(bdev))
 		return ERR_CAST(bdev);
+retry_super:
 	sb = get_super(bdev);
+	if (sb && sb->s_frozen != SB_UNFROZEN) {
+		/*
+		 * When resuming a frozen device, s_umount is taken for write.
+		 * To avoid deadlock, we drop s_umount if the filesystem
+		 * is frozen and wait for it to thaw.
+		 */
+		up_read(&sb->s_umount);
+		vfs_check_frozen(sb, SB_FREEZE_WRITE);
+		put_super(sb);
+		goto retry_super;
+	}
 	bdput(bdev);
 	if (!sb)
 		return ERR_PTR(-ENODEV);
Index: linux-3.1-fast/include/linux/fs.h
===================================================================
--- linux-3.1-fast.orig/include/linux/fs.h	2011-11-25 21:13:56.000000000 +0100
+++ linux-3.1-fast/include/linux/fs.h	2011-11-25 21:14:03.000000000 +0100
@@ -2496,6 +2496,7 @@ extern struct file_system_type *get_fs_t
 extern struct super_block *get_super(struct block_device *);
 extern struct super_block *get_active_super(struct block_device *bdev);
 extern struct super_block *user_get_super(dev_t);
+extern void put_super(struct super_block *sb);
 extern void drop_super(struct super_block *sb);
 extern void iterate_supers(void (*)(struct super_block *, void *), void *);
 extern void iterate_supers_type(struct file_system_type *,