diff mbox series

[04/45] fs: simplify freeze_bdev/thaw_bdev

Message ID 20201124132751.3747337-5-hch@lst.de (mailing list archive)
State New
Headers show
Series [01/45] blk-cgroup: fix a hd_struct leak in blkcg_fill_root_iostats | expand

Commit Message

Christoph Hellwig Nov. 24, 2020, 1:27 p.m. UTC
Store the frozen superblock in struct block_device to avoid the awkward
interface that can return a sb only used a cookie, an ERR_PTR or NULL.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/md/dm-core.h      |  5 -----
 drivers/md/dm.c           | 20 ++++++--------------
 fs/block_dev.c            | 39 ++++++++++++++++-----------------------
 fs/buffer.c               |  2 +-
 fs/ext4/ioctl.c           |  2 +-
 fs/f2fs/file.c            | 14 +++++---------
 fs/xfs/xfs_fsops.c        |  7 ++-----
 include/linux/blk_types.h |  1 +
 include/linux/blkdev.h    |  4 ++--
 9 files changed, 34 insertions(+), 60 deletions(-)

Comments

Chao Yu Nov. 25, 2020, 6:07 a.m. UTC | #1
On 2020/11/24 21:27, Christoph Hellwig wrote:
> Store the frozen superblock in struct block_device to avoid the awkward
> interface that can return a sb only used a cookie, an ERR_PTR or NULL.
> 
> Signed-off-by: Christoph Hellwig<hch@lst.de>
> ---
>   drivers/md/dm-core.h      |  5 -----
>   drivers/md/dm.c           | 20 ++++++--------------
>   fs/block_dev.c            | 39 ++++++++++++++++-----------------------
>   fs/buffer.c               |  2 +-
>   fs/ext4/ioctl.c           |  2 +-
>   fs/f2fs/file.c            | 14 +++++---------

For f2fs part,

Acked-by: Chao Yu <yuchao0@huawei.com>

Thanks,

>   fs/xfs/xfs_fsops.c        |  7 ++-----
>   include/linux/blk_types.h |  1 +
>   include/linux/blkdev.h    |  4 ++--
>   9 files changed, 34 insertions(+), 60 deletions(-)
Jan Kara Nov. 25, 2020, 12:29 p.m. UTC | #2
On Tue 24-11-20 14:27:10, Christoph Hellwig wrote:
> Store the frozen superblock in struct block_device to avoid the awkward
> interface that can return a sb only used a cookie, an ERR_PTR or NULL.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Some comments below...

> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index d8664f5c1ff669..60492620d51866 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -548,55 +548,47 @@ EXPORT_SYMBOL(fsync_bdev);
>   * count down in thaw_bdev(). When it becomes 0, thaw_bdev() will unfreeze
>   * actually.
>   */
> -struct super_block *freeze_bdev(struct block_device *bdev)
> +int freeze_bdev(struct block_device *bdev)
>  {
>  	struct super_block *sb;
>  	int error = 0;
>  
>  	mutex_lock(&bdev->bd_fsfreeze_mutex);
> -	if (++bdev->bd_fsfreeze_count > 1) {
> -		/*
> -		 * We don't even need to grab a reference - the first call
> -		 * to freeze_bdev grab an active reference and only the last
> -		 * thaw_bdev drops it.
> -		 */
> -		sb = get_super(bdev);
> -		if (sb)
> -			drop_super(sb);
> -		mutex_unlock(&bdev->bd_fsfreeze_mutex);
> -		return sb;
> -	}
> +	if (++bdev->bd_fsfreeze_count > 1)
> +		goto done;
>  
>  	sb = get_active_super(bdev);
>  	if (!sb)
> -		goto out;
> +		goto sync;
>  	if (sb->s_op->freeze_super)
>  		error = sb->s_op->freeze_super(sb);
>  	else
>  		error = freeze_super(sb);
> +	deactivate_super(sb);
> +
>  	if (error) {
> -		deactivate_super(sb);
>  		bdev->bd_fsfreeze_count--;
> -		mutex_unlock(&bdev->bd_fsfreeze_mutex);
> -		return ERR_PTR(error);
> +		goto done;
>  	}
> -	deactivate_super(sb);
> - out:
> +	bdev->bd_fsfreeze_sb = sb;
> +
> +sync:
>  	sync_blockdev(bdev);
> +done:
>  	mutex_unlock(&bdev->bd_fsfreeze_mutex);
> -	return sb;	/* thaw_bdev releases s->s_umount */
> +	return error;	/* thaw_bdev releases s->s_umount */

The comment about thaw_bdev() seems to be stale? At least I don't see what
it's speaking about...

>  }
>  EXPORT_SYMBOL(freeze_bdev);
>  
>  /**
>   * thaw_bdev  -- unlock filesystem
>   * @bdev:	blockdevice to unlock
> - * @sb:		associated superblock
>   *
>   * Unlocks the filesystem and marks it writeable again after freeze_bdev().
>   */
> -int thaw_bdev(struct block_device *bdev, struct super_block *sb)
> +int thaw_bdev(struct block_device *bdev)
>  {
> +	struct super_block *sb;
>  	int error = -EINVAL;
>  
>  	mutex_lock(&bdev->bd_fsfreeze_mutex);
> @@ -607,6 +599,7 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
>  	if (--bdev->bd_fsfreeze_count > 0)
>  		goto out;
>  
> +	sb = bdev->bd_fsfreeze_sb;
>  	if (!sb)
>  		goto out;
>  
> @@ -618,7 +611,7 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
>  		bdev->bd_fsfreeze_count++;
>  out:
>  	mutex_unlock(&bdev->bd_fsfreeze_mutex);
> -	return error;
> +	return 0;

But we now won't return -EINVAL if this gets called e.g. with
bd_fsfreeze_count == 0, right?

									Honza
Christoph Hellwig Nov. 25, 2020, 4:22 p.m. UTC | #3
On Wed, Nov 25, 2020 at 01:29:53PM +0100, Jan Kara wrote:
> >  	mutex_unlock(&bdev->bd_fsfreeze_mutex);
> > -	return sb;	/* thaw_bdev releases s->s_umount */
> > +	return error;	/* thaw_bdev releases s->s_umount */
> 
> The comment about thaw_bdev() seems to be stale? At least I don't see what
> it's speaking about...

Yes, this comment seems long stale.  I think in the very early days
we held s_umount on frozen file system, which caused all kinds of
problems.

> >  	mutex_unlock(&bdev->bd_fsfreeze_mutex);
> > -	return error;
> > +	return 0;
> 
> But we now won't return -EINVAL if this gets called e.g. with
> bd_fsfreeze_count == 0, right?

Yes.  I had tried to drop the return value as all the freeze_bdev
calls ignored it.  But I had missed the unpaired emergency thaw and put
it back and messed this up..
diff mbox series

Patch

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index d522093cb39dda..aace147effcacb 100644
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -96,11 +96,6 @@  struct mapped_device {
 	 */
 	struct workqueue_struct *wq;
 
-	/*
-	 * freeze/thaw support require holding onto a super block
-	 */
-	struct super_block *frozen_sb;
-
 	/* forced geometry settings */
 	struct hd_geometry geometry;
 
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 54739f1b579bc8..50541d336c719b 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2392,27 +2392,19 @@  static int lock_fs(struct mapped_device *md)
 {
 	int r;
 
-	WARN_ON(md->frozen_sb);
+	WARN_ON(test_bit(DMF_FROZEN, &md->flags));
 
-	md->frozen_sb = freeze_bdev(md->bdev);
-	if (IS_ERR(md->frozen_sb)) {
-		r = PTR_ERR(md->frozen_sb);
-		md->frozen_sb = NULL;
-		return r;
-	}
-
-	set_bit(DMF_FROZEN, &md->flags);
-
-	return 0;
+	r = freeze_bdev(md->bdev);
+	if (!r)
+		set_bit(DMF_FROZEN, &md->flags);
+	return r;
 }
 
 static void unlock_fs(struct mapped_device *md)
 {
 	if (!test_bit(DMF_FROZEN, &md->flags))
 		return;
-
-	thaw_bdev(md->bdev, md->frozen_sb);
-	md->frozen_sb = NULL;
+	thaw_bdev(md->bdev);
 	clear_bit(DMF_FROZEN, &md->flags);
 }
 
diff --git a/fs/block_dev.c b/fs/block_dev.c
index d8664f5c1ff669..60492620d51866 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -548,55 +548,47 @@  EXPORT_SYMBOL(fsync_bdev);
  * count down in thaw_bdev(). When it becomes 0, thaw_bdev() will unfreeze
  * actually.
  */
-struct super_block *freeze_bdev(struct block_device *bdev)
+int freeze_bdev(struct block_device *bdev)
 {
 	struct super_block *sb;
 	int error = 0;
 
 	mutex_lock(&bdev->bd_fsfreeze_mutex);
-	if (++bdev->bd_fsfreeze_count > 1) {
-		/*
-		 * We don't even need to grab a reference - the first call
-		 * to freeze_bdev grab an active reference and only the last
-		 * thaw_bdev drops it.
-		 */
-		sb = get_super(bdev);
-		if (sb)
-			drop_super(sb);
-		mutex_unlock(&bdev->bd_fsfreeze_mutex);
-		return sb;
-	}
+	if (++bdev->bd_fsfreeze_count > 1)
+		goto done;
 
 	sb = get_active_super(bdev);
 	if (!sb)
-		goto out;
+		goto sync;
 	if (sb->s_op->freeze_super)
 		error = sb->s_op->freeze_super(sb);
 	else
 		error = freeze_super(sb);
+	deactivate_super(sb);
+
 	if (error) {
-		deactivate_super(sb);
 		bdev->bd_fsfreeze_count--;
-		mutex_unlock(&bdev->bd_fsfreeze_mutex);
-		return ERR_PTR(error);
+		goto done;
 	}
-	deactivate_super(sb);
- out:
+	bdev->bd_fsfreeze_sb = sb;
+
+sync:
 	sync_blockdev(bdev);
+done:
 	mutex_unlock(&bdev->bd_fsfreeze_mutex);
-	return sb;	/* thaw_bdev releases s->s_umount */
+	return error;	/* thaw_bdev releases s->s_umount */
 }
 EXPORT_SYMBOL(freeze_bdev);
 
 /**
  * thaw_bdev  -- unlock filesystem
  * @bdev:	blockdevice to unlock
- * @sb:		associated superblock
  *
  * Unlocks the filesystem and marks it writeable again after freeze_bdev().
  */
-int thaw_bdev(struct block_device *bdev, struct super_block *sb)
+int thaw_bdev(struct block_device *bdev)
 {
+	struct super_block *sb;
 	int error = -EINVAL;
 
 	mutex_lock(&bdev->bd_fsfreeze_mutex);
@@ -607,6 +599,7 @@  int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 	if (--bdev->bd_fsfreeze_count > 0)
 		goto out;
 
+	sb = bdev->bd_fsfreeze_sb;
 	if (!sb)
 		goto out;
 
@@ -618,7 +611,7 @@  int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 		bdev->bd_fsfreeze_count++;
 out:
 	mutex_unlock(&bdev->bd_fsfreeze_mutex);
-	return error;
+	return 0;
 }
 EXPORT_SYMBOL(thaw_bdev);
 
diff --git a/fs/buffer.c b/fs/buffer.c
index 23f645657488ba..a7595ada9400ff 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -523,7 +523,7 @@  static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 
 void emergency_thaw_bdev(struct super_block *sb)
 {
-	while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
+	while (sb->s_bdev && !thaw_bdev(sb->s_bdev))
 		printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
 }
 
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index f0381876a7e5b0..524e134324475e 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -624,7 +624,7 @@  static int ext4_shutdown(struct super_block *sb, unsigned long arg)
 	case EXT4_GOING_FLAGS_DEFAULT:
 		freeze_bdev(sb->s_bdev);
 		set_bit(EXT4_FLAGS_SHUTDOWN, &sbi->s_ext4_flags);
-		thaw_bdev(sb->s_bdev, sb);
+		thaw_bdev(sb->s_bdev);
 		break;
 	case EXT4_GOING_FLAGS_LOGFLUSH:
 		set_bit(EXT4_FLAGS_SHUTDOWN, &sbi->s_ext4_flags);
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ee861c6d9ff026..a9fc482a0e60a5 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2230,16 +2230,12 @@  static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
 
 	switch (in) {
 	case F2FS_GOING_DOWN_FULLSYNC:
-		sb = freeze_bdev(sb->s_bdev);
-		if (IS_ERR(sb)) {
-			ret = PTR_ERR(sb);
+		ret = freeze_bdev(sb->s_bdev);
+		if (ret)
 			goto out;
-		}
-		if (sb) {
-			f2fs_stop_checkpoint(sbi, false);
-			set_sbi_flag(sbi, SBI_IS_SHUTDOWN);
-			thaw_bdev(sb->s_bdev, sb);
-		}
+		f2fs_stop_checkpoint(sbi, false);
+		set_sbi_flag(sbi, SBI_IS_SHUTDOWN);
+		thaw_bdev(sb->s_bdev);
 		break;
 	case F2FS_GOING_DOWN_METASYNC:
 		/* do checkpoint only */
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index ef1d5bb88b93ab..b7c5783a031c69 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -433,13 +433,10 @@  xfs_fs_goingdown(
 {
 	switch (inflags) {
 	case XFS_FSOP_GOING_FLAGS_DEFAULT: {
-		struct super_block *sb = freeze_bdev(mp->m_super->s_bdev);
-
-		if (sb && !IS_ERR(sb)) {
+		if (!freeze_bdev(mp->m_super->s_bdev)) {
 			xfs_force_shutdown(mp, SHUTDOWN_FORCE_UMOUNT);
-			thaw_bdev(sb->s_bdev, sb);
+			thaw_bdev(mp->m_super->s_bdev);
 		}
-
 		break;
 	}
 	case XFS_FSOP_GOING_FLAGS_LOGFLUSH:
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d9b69bbde5cc54..ebfb4e7c1fd125 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -46,6 +46,7 @@  struct block_device {
 	int			bd_fsfreeze_count;
 	/* Mutex for freeze */
 	struct mutex		bd_fsfreeze_mutex;
+	struct super_block	*bd_fsfreeze_sb;
 } __randomize_layout;
 
 /*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 05b346a68c2eee..12810a19edebc4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -2020,7 +2020,7 @@  static inline int sync_blockdev(struct block_device *bdev)
 #endif
 int fsync_bdev(struct block_device *bdev);
 
-struct super_block *freeze_bdev(struct block_device *bdev);
-int thaw_bdev(struct block_device *bdev, struct super_block *sb);
+int freeze_bdev(struct block_device *bdev);
+int thaw_bdev(struct block_device *bdev);
 
 #endif /* _LINUX_BLKDEV_H */