From 48b6bca6b7b8309697fc8a101793befe92d249d9 Mon Sep 17 00:00:00 2001 From: Benjamin Marzinski Date: Thu, 13 Nov 2014 20:42:03 -0600 Subject: [PATCH] fs: add freeze_super/thaw_super fs hooks 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. Reviewed-by: Jan Kara Signed-off-by: Benjamin Marzinski Signed-off-by: Steven Whitehouse --- 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 1d9c9f3754f8..b48c41bf0f86 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -235,7 +235,10 @@ 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--; @@ -272,7 +275,10 @@ 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 8ac3fad36192..77c9a7812542 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 9ab779e8a63c..b4a1d73c0d5d 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1577,7 +1577,9 @@ 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 *);