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Subject[PATCH 2/2] quota: Fix deadlock with suspend and quotas
Date
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>
---
fs/quota/quota.c | 24 +++++++++++++++++++++---
1 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index 7898cd6..fc2c438 100644
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -292,11 +292,26 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
}
}

+/* Return 1 if 'cmd' will block on frozen filesystem */
+static int quotactl_cmd_write(int cmd)
+{
+ switch (cmd) {
+ case Q_GETFMT:
+ case Q_GETINFO:
+ case Q_SYNC:
+ case Q_XGETQSTAT:
+ case Q_XGETQUOTA:
+ case Q_XQUOTASYNC:
+ return 0;
+ }
+ return 1;
+}
+
/*
* look up a superblock on which quota ops will be performed
* - use the name of a block device to find the superblock thereon
*/
-static struct super_block *quotactl_block(const char __user *special)
+static struct super_block *quotactl_block(const char __user *special, int cmd)
{
#ifdef CONFIG_BLOCK
struct block_device *bdev;
@@ -309,7 +324,10 @@ static struct super_block *quotactl_block(const char __user *special)
putname(tmp);
if (IS_ERR(bdev))
return ERR_CAST(bdev);
- sb = get_super(bdev);
+ if (quotactl_cmd_write(cmd))
+ sb = get_super_thawed(bdev);
+ else
+ sb = get_super(bdev);
bdput(bdev);
if (!sb)
return ERR_PTR(-ENODEV);
@@ -361,7 +379,7 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
pathp = &path;
}

- sb = quotactl_block(special);
+ sb = quotactl_block(special, cmds);
if (IS_ERR(sb)) {
ret = PTR_ERR(sb);
goto out;
--
1.7.1


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