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freeze feature ver 1.0

RFC PATCH In review Takashi Sato 2 participants 2 messages Mar 24, 2008 – Mar 25, 2008

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Takashi Sato

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RFC PATCH 1/1 freeze feature ver 1.0

Hi,

This is the rebased freeze feature patch for linux-2.6.25-rc6. We can take a backup which keeps the filesystem's consistency with it. I have tested it cooperating with
DRBD (Distributed Replicated Block Device (http://www.drbd.org/))
and made sure that I could take the consistent backup with a short frozen time (several seconds) while using the filesystem. The detailed procedure for my test is below.

1. Set up the replication between server A (primary) and server B (secondary)

2. Make the ext3 filesystem on server A and mount it (Run Linux kernel compile by 5 threads in parallel on it)

3. Freeze the filesystem on server A to block I/O and keep the filesystem's consistency

4. Detach the secondary volume on server B
(e.g /sbin/drbdadm detach r0)

5. Unfreeze the filesystem on server A

6. Use the secondary volume on server B
I confirmed the followings.
- fsck didn't report any errors.
- It could be mounted correctly.
- Linux kernel compiles could re-start correctly.

There is no functional change from the previous version. All of comments from ML have already been reflected in this patch.

The ioctls for the freeze feature are below.
o Freeze the filesystem
int ioctl(int fd, int FIFREEZE, long *timeval)
fd: The file descriptor of the mountpoint
FIFREEZE: request code for the freeze
timeval: the timeout period in seconds
If it's 0 or 1, the timeout isn't set. This special case of "1" is implemented to keep the compatibility with XFS applications.
Return value: 0 if the operation succeeds. Otherwise, -1

o Reset the timeout period
This is useful for the application to set the timeval more accurately. For example, the freezer resets the timeval to 10 seconds every 5 seconds. In this approach, even if the freezer causes a deadlock by accessing the frozen filesystem, it will be solved by the timeout in 10 seconds and the freezer can recognize that at the next reset of timeval.
int ioctl(int fd, int FIFREEZE_RESET_TIMEOUT, long *timeval)
fd:file descriptor of mountpoint
FIFREEZE_RESET_TIMEOUT: request code for reset of timeout period
timeval: new timeout period in seconds
Return value: 0 if the operation succeeds. Otherwise, -1 Error number: If the filesystem has already been unfrozen,
errno is set to EINVAL.

o Unfreeze the filesystem
int ioctl(int fd, int FITHAW, long *timeval)
fd: The file descriptor of the mountpoint
FITHAW: request code for unfreeze
timeval: Ignored
Return value: 0 if the operation succeeds. Otherwise, -1

Any comments are very welcome.

Cheers, Takashi

Signed-off-by Takashi Sato <[email protected]>

---
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc6.org/drivers/md/dm.c linux-2.6.25-rc6-freeze/drivers/ md/dm.c

drivers/md/dm.c +1 -1
@@ -1407,7 +1407,7 @@ static int lock_fs(struct mapped_device 
 
 	WARN_ON(md->frozen_sb);
 
-	md->frozen_sb = freeze_bdev(md->suspended_bdev);
+	md->frozen_sb = freeze_bdev(md->suspended_bdev, 0);
 	if (IS_ERR(md->frozen_sb)) {
 		r = PTR_ERR(md->frozen_sb);
 		md->frozen_sb = NULL;

diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc6.org/fs/block_dev.c linux-2.6.25-rc6-freeze/fs/block_ dev.c

fs/block_dev.c +5 -0
@@ -284,6 +284,11 @@ static void init_once(struct kmem_cache 
 	INIT_LIST_HEAD(&bdev->bd_holder_list);
 #endif
 	inode_init_once(&ei->vfs_inode);
+
+	/* Initialize semaphore for freeze. */
+	sema_init(&bdev->bd_freeze_sem, 1);
+	/* Setup freeze timeout function. */
+	INIT_DELAYED_WORK(&bdev->bd_freeze_timeout, freeze_timeout);
 }
 
 static inline void __bd_forget(struct inode *inode)
fs/buffer.c +37 -2
diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc6.org/fs/buffer.c linux-2.6.25-rc6-freeze/fs/buffer.c
@@ -190,17 +190,33 @@ int fsync_bdev(struct block_device *bdev
 
 /**
  * freeze_bdev  --  lock a filesystem and force it into a consistent state
- * @bdev:	blockdevice to lock
+ * @bdev:		blockdevice to lock
+ * @timeout_msec:	timeout period
  *
  * 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.
+ * If timeout_msec is bigger than 0, this registers the delayed work for
+ * timeout of the freeze feature.
  */
-struct super_block *freeze_bdev(struct block_device *bdev)
+struct super_block *freeze_bdev(struct block_device *bdev, long timeout_msec)
 {
 	struct super_block *sb;
 
+	down(&bdev->bd_freeze_sem);
+	sb = get_super_without_lock(bdev);
+
+	/* If super_block has been already frozen, return. */
+	if (sb && sb->s_frozen != SB_UNFROZEN) {
+		put_super(sb);
+		up(&bdev->bd_freeze_sem);
+		return sb;
+	}
+
+	if (sb)
+		put_super(sb);
+
 	down(&bdev->bd_mount_sem);
 	sb = get_super(bdev);
 	if (sb && !(sb->s_flags & MS_RDONLY)) {

@@ -219,6 +235,13 @@ struct super_block *freeze_bdev(struct b
 	}
 
 	sync_blockdev(bdev);
+
+	/* Setup unfreeze timer. */
+	if (timeout_msec > 0)
+		add_freeze_timeout(bdev, timeout_msec);
+
+	up(&bdev->bd_freeze_sem);
+
 	return sb;	/* thaw_bdev releases s->s_umount and bd_mount_sem */
 }
 EXPORT_SYMBOL(freeze_bdev);

@@ -232,6 +255,16 @@ EXPORT_SYMBOL(freeze_bdev);
  */
 void thaw_bdev(struct block_device *bdev, struct super_block *sb)
 {
+	down(&bdev->bd_freeze_sem);
+
+	if (sb && sb->s_frozen == SB_UNFROZEN) {
+		up(&bdev->bd_freeze_sem);
+		return;
+	}
+
+	/* Delete unfreeze timer. */
+	del_freeze_timeout(bdev);
+
 	if (sb) {
 		BUG_ON(sb->s_bdev != bdev);
 

@@ -244,6 +277,8 @@ void thaw_bdev(struct block_device *bdev
 	}
 
 	up(&bdev->bd_mount_sem);
+
+	up(&bdev->bd_freeze_sem);
 }
 EXPORT_SYMBOL(thaw_bdev);
fs/ioctl.c +97 -0

109 lines not on this page · raw message

fs/super.c +83 -1

99 lines not on this page · raw message

diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc6.org/fs/xfs/linux-2.6/xfs_ioctl.c linux-2.6.25-rc6-fr eeze/fs/xfs/linux-2.6/xfs_ioctl.c

fs/xfs/linux-2.6/xfs_ioctl.c +1 -1
@@ -911,7 +911,7 @@ xfs_ioctl(
 			return -EPERM;
 
 		if (inode->i_sb->s_frozen == SB_UNFROZEN)
-			freeze_bdev(inode->i_sb->s_bdev);
+			freeze_bdev(inode->i_sb->s_bdev, 0);
 		return 0;
 
 	case XFS_IOC_THAW:

diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc6.org/fs/xfs/xfs_fsops.c linux-2.6.25-rc6-freeze/fs/xf s/xfs_fsops.c

fs/xfs/xfs_fsops.c +1 -1
@@ -623,7 +623,7 @@ xfs_fs_goingdown(
 {
 	switch (inflags) {
 	case XFS_FSOP_GOING_FLAGS_DEFAULT: {
-		struct super_block *sb = freeze_bdev(mp->m_super->s_bdev);
+		struct super_block *sb = freeze_bdev(mp->m_super->s_bdev, 0);
 
 		if (sb && !IS_ERR(sb)) {
 			xfs_force_shutdown(mp, SHUTDOWN_FORCE_UMOUNT);

diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc6.org/include/linux/buffer_head.h linux-2.6.25-rc6-fre eze/include/linux/buffer_head.h

include/linux/buffer_head.h +1 -1
@@ -170,7 +170,7 @@ int sync_blockdev(struct block_device *b
 void __wait_on_buffer(struct buffer_head *);
 wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
 int fsync_bdev(struct block_device *);
-struct super_block *freeze_bdev(struct block_device *);
+struct super_block *freeze_bdev(struct block_device *, long timeout_msec);
 void thaw_bdev(struct block_device *, struct super_block *);
 int fsync_super(struct super_block *);
 int fsync_no_super(struct block_device *);

diff -uprN -X /home/sho/pub/MC/freeze-set/dontdiff linux-2.6.25-rc6.org/include/linux/fs.h linux-2.6.25-rc6-freeze/inclu de/linux/fs.h

include/linux/fs.h +15 -0
@@ -8,6 +8,7 @@
 
 #include <linux/limits.h>
 #include <linux/ioctl.h>
+#include <linux/workqueue.h>
 
 /*
  * It's silly to have NR_OPEN bigger than NR_FILE, but you can change

@@ -223,6 +224,9 @@ extern int dir_notify_enable;
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */
 #define FIGETBSZ   _IO(0x00,2)	/* get the block size used for bmap */
+#define FIFREEZE	_IOWR('X', 119, int)	/* Freeze */
+#define FITHAW		_IOWR('X', 120, int)	/* Thaw */
+#define	FIFREEZE_RESET_TIMEOUT	_IO(0x00, 3)	/* Reset freeze timeout */
 
 #define	FS_IOC_GETFLAGS			_IOR('f', 1, long)
 #define	FS_IOC_SETFLAGS			_IOW('f', 2, long)

@@ -548,6 +552,11 @@ struct block_device {
 	 * care to not mess up bd_private for that case.
 	 */
 	unsigned long		bd_private;
+
+	/* Delayed work for freeze */
+	struct delayed_work	bd_freeze_timeout;
+	/* Semaphore for freeze */
+	struct semaphore	bd_freeze_sem;
 };
 
 /*

@@ -1926,7 +1935,9 @@ extern int do_vfs_ioctl(struct file *fil
 extern void get_filesystem(struct file_system_type *fs);
 extern void put_filesystem(struct file_system_type *fs);
 extern struct file_system_type *get_fs_type(const char *name);
+extern void put_super(struct super_block *sb);
 extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_super_without_lock(struct block_device *);
 extern struct super_block *user_get_super(dev_t);
 extern void drop_super(struct super_block *sb);
 

@@ -2097,5 +2108,9 @@ int proc_nr_files(struct ctl_table *tabl
 
 int get_filesystem_list(char * buf);
 
+extern void add_freeze_timeout(struct block_device *bdev, long timeout_msec);
+extern void del_freeze_timeout(struct block_device *bdev);
+extern void freeze_timeout(struct work_struct *work);
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_FS_H */
#1 lore raw
Quoted 24 lines · Takashi Sato

Hi,

This is the rebased freeze feature patch for linux-2.6.25-rc6. We can take a backup which keeps the filesystem's consistency with it. I have tested it cooperating with
DRBD (Distributed Replicated Block Device (http://www.drbd.org/))
and made sure that I could take the consistent backup with a short frozen time (several seconds) while using the filesystem. The detailed procedure for my test is below.

1. Set up the replication between server A (primary) and server B (secondary)

2. Make the ext3 filesystem on server A and mount it (Run Linux kernel compile by 5 threads in parallel on it)

3. Freeze the filesystem on server A to block I/O and keep the filesystem's consistency

4. Detach the secondary volume on server B
(e.g /sbin/drbdadm detach r0)

5. Unfreeze the filesystem on server A

Quoted 8 lines

6. Use the secondary volume on server B
I confirmed the followings.
- fsck didn't report any errors.
- It could be mounted correctly.
- Linux kernel compiles could re-start correctly.

There is no functional change from the previous version. All of comments from ML have already been reflected in this patch.

Can you please split this into two patches - one which introduces the generic functionality *without* the timeout stuff, and a second patch that introduces the timeouts.

I think this timeout stuff is dangerous - it adds significant complexity and really does not protect against anything that can't be done in userspace. i.e. If your system is running well enough for the timer to fire and unfreeze the filesystem, it's running well enough for you to do "freeze X; sleep Y; unfreeze X". If you are trying to protect against a freeze operation that hangs then the filesystem needs fixing, not some new API to work around a bug....

FWIW, there is nothing to guarantee that the filesystem has finished freezing when the timeout fires (it's not uncommon to see freeze_bdev() taking *minutes*) and unfreezing in the middle of a freeze operation will cause problems - either for the filesystem in the middle of a freeze operation, or for whatever is freezing the filesystem to get a consistent image.....

Cheers,

Dave.

Signature · 3 lines
Dave Chinner
Principal Engineer
SGI Australian Software Group