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Subject[PATCH] deadlock with suspend and quotas
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@redhat.com>
CC: stable@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 *,

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