[PATCH] fs: ioctl_fsthaw should use freeze_bdev if possible

[Dmitry Monakhov <dmonakhov@openvz.org>]

Commit: 18e9e5104fcd  breaks connection between freeze_bdev()/thaw_bdev() and
freeze_super()/thaw_super()
In other workds:
freeze_bdev()/thaw_bdev() may be called multiple times, but
freeze_super()/thaw_super() only once (will resunt -EBUSY on second call)

BUT user is still allowed to mix both interfaces:

freeze_bdev () call it first time
 ->bdev->bd_fsfreeze_count++
 ->freeze_super()
   return 0
freeze_super() second time
 ->bdev->bd_fsfreeze_count++
   return 0

One can call ioctl_fsthaw( #xfs_freeze -u $MNT)
ioctl_fsthaw
 ->thaw_super() -> fs is unfrozen now
   return 0

This leave bdev in broken state because:
bd_fsfreeze_count > 0 but superblock is not frozen.
Visiable effect:
0) Any freeze_bdev() will not call freeze_super() because
   (bdev->bd_fsfreeze_count > 0)
1) thaw_bdev() will fail because thaw_super() will return EINVAL (filesystem
   is not frozen) and bdev->bd_fsfreeze_count will not being decremented.
2) filesystem may not being mounted because mount_bdev will fail
   because (bdev->bd_fsfreeze_count > 0)

#TEST_CASE:
# Use xfstests 068'th test
(while true ;do dmsetup suspend $SCRATCH_DEV ;dmsetup resume $SCRATCH_DEV;done)&
pid=$!
./check 068 068 068 068 068
kill $pid
wait $pid

In order to fix that let's always use {freeze,thaw}_bdev() functions if
super block has bdev, and directly call {freeze,thaw)_super() otherwise.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
 fs/ioctl.c |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/ioctl.c b/fs/ioctl.c
index 3bdad6d..ea47ccc 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -513,6 +513,7 @@ static int ioctl_fioasync(unsigned int fd, struct file *filp,
 static int ioctl_fsfreeze(struct file *filp)
 {
 	struct super_block *sb = filp->f_path.dentry->d_inode->i_sb;
+	int ret = 0;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -521,8 +522,15 @@ static int ioctl_fsfreeze(struct file *filp)
 	if (sb->s_op->freeze_fs == NULL)
 		return -EOPNOTSUPP;
 
-	/* Freeze */
-	return freeze_super(sb);
+	if (sb->s_bdev) {
+		struct super_block *fsb;
+		fsb = freeze_bdev(sb->s_bdev);
+		if (IS_ERR(fsb))
+			ret = PTR_ERR(fsb);
+	} else {
+		ret = freeze_super(sb);
+	}
+	return ret;
 }
 
 static int ioctl_fsthaw(struct file *filp)
@@ -532,7 +540,9 @@ static int ioctl_fsthaw(struct file *filp)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	/* Thaw */
+	if (sb->s_bdev)
+		return thaw_bdev(sb->s_bdev, sb);
+
 	return thaw_super(sb);
 }
 
-- 
1.7.1