Now that we have the freeze count there is not much reason for bd_mount_sem
anymore. The actual freeze/thaw operations are serialized using the
bd_fsfreeze_mutex, and the only other place we take bd_mount_sem is
get_sb_bdev which tries to prevent mounting a filesystem while the block
device is frozen. Instead of add a check for bd_fsfreeze_count and
return -EBUSY if a filesystem is frozen. While that is a change in user
visible behaviour a failing mount is much better for this case rather
than having the mount process stuck uninterruptible for a long time.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Index: linux-2.6/fs/block_dev.c
===================================================================
--- linux-2.6.orig/fs/block_dev.c 2009-08-01 21:05:06.257330315 +0200
+++ linux-2.6/fs/block_dev.c 2009-08-01 21:08:57.094353741 +0200
@@ -216,8 +216,6 @@ EXPORT_SYMBOL(fsync_bdev);
* freeze_bdev -- lock a filesystem and force it into a consistent state
* @bdev: blockdevice to lock
*
- * This takes the block device bd_mount_sem to make sure no new mounts
- * happen on bdev until thaw_bdev() is called.
* If a superblock is found on this device, we take the s_umount semaphore
* on it to make sure nobody unmounts until the snapshot creation is done.
* The reference counter (bd_fsfreeze_count) guarantees that only the last
@@ -240,7 +238,6 @@ struct super_block *freeze_bdev(struct b
}
bdev->bd_fsfreeze_count++;
- down(&bdev->bd_mount_sem);
sb = get_super(bdev);
if (sb && !(sb->s_flags & MS_RDONLY)) {
sb->s_frozen = SB_FREEZE_WRITE;
@@ -260,7 +257,6 @@ struct super_block *freeze_bdev(struct b
"VFS:Filesystem freeze failed\n");
sb->s_frozen = SB_UNFROZEN;
drop_super(sb);
- up(&bdev->bd_mount_sem);
bdev->bd_fsfreeze_count--;
mutex_unlock(&bdev->bd_fsfreeze_mutex);
return ERR_PTR(error);
@@ -271,7 +267,7 @@ struct super_block *freeze_bdev(struct b
sync_blockdev(bdev);
mutex_unlock(&bdev->bd_fsfreeze_mutex);
- return sb; /* thaw_bdev releases s->s_umount and bd_mount_sem */
+ return sb; /* thaw_bdev releases s->s_umount */
}
EXPORT_SYMBOL(freeze_bdev);
@@ -321,7 +317,6 @@ int thaw_bdev(struct block_device *bdev,
drop_super(sb);
}
- up(&bdev->bd_mount_sem);
mutex_unlock(&bdev->bd_fsfreeze_mutex);
return 0;
}
@@ -431,7 +426,6 @@ static void init_once(void *foo)
memset(bdev, 0, sizeof(*bdev));
mutex_init(&bdev->bd_mutex);
- sema_init(&bdev->bd_mount_sem, 1);
INIT_LIST_HEAD(&bdev->bd_inodes);
INIT_LIST_HEAD(&bdev->bd_list);
#ifdef CONFIG_SYSFS
Index: linux-2.6/fs/super.c
===================================================================
--- linux-2.6.orig/fs/super.c 2009-08-01 21:05:06.264331137 +0200
+++ linux-2.6/fs/super.c 2009-08-01 21:08:57.094353741 +0200
@@ -740,9 +740,14 @@ int get_sb_bdev(struct file_system_type
* will protect the lockfs code from trying to start a snapshot
* while we are mounting
*/
- down(&bdev->bd_mount_sem);
+ mutex_lock(&bdev->bd_fsfreeze_mutex);
+ if (bdev->bd_fsfreeze_count > 0) {
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
+ error = -EBUSY;
+ goto error_bdev;
+ }
s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
- up(&bdev->bd_mount_sem);
+ mutex_unlock(&bdev->bd_fsfreeze_mutex);
if (IS_ERR(s))
goto error_s;
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h 2009-08-01 21:05:06.271330981 +0200
+++ linux-2.6/include/linux/fs.h 2009-08-01 21:08:57.098355019 +0200
@@ -640,7 +640,6 @@ struct block_device {
struct super_block * bd_super;
int bd_openers;
struct mutex bd_mutex; /* open/close mutex */
- struct semaphore bd_mount_sem;
struct list_head bd_inodes;
void * bd_holder;
int bd_holders;
--
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