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 prepare_freeze prepare_thaw
hooks. If a filesystem implements these hooks, they are called instead of
freeze_super and thaw_super. This means that every filesystem that
implements prepare_freeze/thaw must call freeze/thaw_super within that
function to make use of the vfs freezing code.
Signed-off-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
---
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..f931412 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->prepare_freeze)
+ error = sb->s_op->prepare_freeze(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->prepare_thaw)
+ error = sb->s_op->prepare_thaw(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..3eaca46c 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->prepare_freeze == NULL)
return -EOPNOTSUPP;
/* Freeze */
+ if (sb->s_op->prepare_freeze)
+ return sb->s_op->prepare_freeze(sb);
return freeze_super(sb);
}
@@ -533,6 +535,8 @@ static int ioctl_fsthaw(struct file *filp)
return -EPERM;
/* Thaw */
+ if (sb->s_op->prepare_thaw)
+ return sb->s_op->prepare_thaw(sb);
return thaw_super(sb);
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9418772..8d0c577 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 (*prepare_freeze) (struct super_block *);
int (*freeze_fs) (struct super_block *);
+ int (*prepare_thaw) (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
--
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