On Mon 06-10-14 15:12:08, Benjamin Marzinski wrote:
> Currently, freezing a filesystem involves calling freeze_super, which locks
> sb->s_umount and then calls the fs-specific freeze_fs hook. This makes it
> hard for gfs2 (and potentially other cluster filesystems) to use the vfs
> freezing code to do freezes on all the cluster nodes.
>
> In order to communicate that a freeze has been requested, and to make sure
> that only one node is trying to freeze at a time, gfs2 uses a glock
> (sd_freeze_gl). The problem is that there is no hook for gfs2 to acquire
> this lock before calling freeze_super. This means that two nodes can
> attempt to freeze the filesystem by both calling freeze_super, acquiring
> the sb->s_umount lock, and then attempting to grab the cluster glock
> sd_freeze_gl. Only one will succeed, and the other will be stuck in
> freeze_super, making it impossible to finish freezing the node.
>
> To solve this problem, this patch adds the freeze_super and thaw_super
> hooks. If a filesystem implements these hooks, they are called instead of
> the vfs freeze_super and thaw_super functions. This means that every
> filesystem that implements these hooks must call the vfs freeze_super and
> thaw_super functions itself within the hook function to make use of the vfs
> freezing code.
>
> Signed-off-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/block_dev.c | 10 ++++++++--
> fs/ioctl.c | 6 +++++-
> include/linux/fs.h | 2 ++
> 3 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 6d72746..febd57c 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -245,7 +245,10 @@ struct super_block *freeze_bdev(struct block_device *bdev)
> sb = get_active_super(bdev);
> if (!sb)
> goto out;
> - error = freeze_super(sb);
> + if (sb->s_op->freeze_super)
> + error = sb->s_op->freeze_super(sb);
> + else
> + error = freeze_super(sb);
> if (error) {
> deactivate_super(sb);
> bdev->bd_fsfreeze_count--;
> @@ -282,7 +285,10 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
> if (!sb)
> goto out;
>
> - error = thaw_super(sb);
> + if (sb->s_op->thaw_super)
> + error = sb->s_op->thaw_super(sb);
> + else
> + error = thaw_super(sb);
> if (error) {
> bdev->bd_fsfreeze_count++;
> mutex_unlock(&bdev->bd_fsfreeze_mutex);
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 8ac3fad..77c9a78 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -518,10 +518,12 @@ static int ioctl_fsfreeze(struct file *filp)
> return -EPERM;
>
> /* If filesystem doesn't support freeze feature, return. */
> - if (sb->s_op->freeze_fs == NULL)
> + if (sb->s_op->freeze_fs == NULL && sb->s_op->freeze_super == NULL)
> return -EOPNOTSUPP;
>
> /* Freeze */
> + if (sb->s_op->freeze_super)
> + return sb->s_op->freeze_super(sb);
> return freeze_super(sb);
> }
>
> @@ -533,6 +535,8 @@ static int ioctl_fsthaw(struct file *filp)
> return -EPERM;
>
> /* Thaw */
> + if (sb->s_op->thaw_super)
> + return sb->s_op->thaw_super(sb);
> return thaw_super(sb);
> }
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 9418772..1d1e07d 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1570,7 +1570,9 @@ struct super_operations {
> void (*evict_inode) (struct inode *);
> void (*put_super) (struct super_block *);
> int (*sync_fs)(struct super_block *sb, int wait);
> + int (*freeze_super) (struct super_block *);
> int (*freeze_fs) (struct super_block *);
> + int (*thaw_super) (struct super_block *);
> int (*unfreeze_fs) (struct super_block *);
> int (*statfs) (struct dentry *, struct kstatfs *);
> int (*remount_fs) (struct super_block *, int *, char *);
> --
> 1.8.3.1
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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