sandeen at sandeen
Feb 9, 2012, 8:46 AM
Post #2 of 3
(33 views)
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Re: [PATCH 2/2] quota: Fix deadlock with suspend and quotas
[In reply to]
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On 2/7/12 4:37 PM, Jan Kara wrote:
> 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 [at] redhat>
> Signed-off-by: Jan Kara <jack [at] suse>
Makes sense to me, thanks.
Reviewed-by: Eric Sandeen <sandeen [at] redhat>
> ---
> 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;
--
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