Re: [PATCH 1/3] Implement generic freeze feature

Christoph Hellwig
2008-09-08T17:09:25Z

On Mon, Sep 08, 2008 at 08:52:45PM +0900, Takashi Sato wrote:
> diff -uprN -X linux-2.6.27-rc5.org/Documentation/dontdiff linux-2.6.27-rc5.org/fs/block_dev.c linux-2.6.27-rc5-freeze/fs
> /block_dev.c
> --- linux-2.6.27-rc5.org/fs/block_dev.c 2008-08-29 07:52:02.000000000 +0900
> +++ linux-2.6.27-rc5-freeze/fs/block_dev.c 2008-09-05 20:00:29.000000000 +0900
> @@ -285,6 +285,8 @@ static void init_once(void *foo)
> INIT_LIST_HEAD(&bdev->bd_holder_list);
> #endif
> inode_init_once(&ei->vfs_inode);
> + /* Initialize mutex for freeze. */
> + mutex_init(&bdev->bd_fsfreeze_mutex);

Why not just freeze_mutex?

> struct super_block *freeze_bdev(struct block_device *bdev)
> {
> struct super_block *sb;
>
> + mutex_lock(&bdev->bd_fsfreeze_mutex);
> + if (bdev->bd_fsfreeze_count > 0) {
> + bdev->bd_fsfreeze_count++;
> + sb = get_super(bdev);
> + mutex_unlock(&bdev->bd_fsfreeze_mutex);
> + return sb;
> + }
> + bdev->bd_fsfreeze_count++;
> +
> down(&bdev->bd_mount_sem);

Note that we still have duplication with the bd_mount_sem. I think
you should look into getting rid of it and instead do a check of
the freeze_count under proper freeze_mutex protection.

> +int thaw_bdev(struct block_device *bdev, struct super_block *sb)
> {
> + mutex_lock(&bdev->bd_fsfreeze_mutex);
> + if (!bdev->bd_fsfreeze_count) {
> + mutex_unlock(&bdev->bd_fsfreeze_mutex);
> + return 0;
> + }
> +
> + bdev->bd_fsfreeze_count--;
> + if (bdev->bd_fsfreeze_count > 0) {
> + if (sb)
> + drop_super(sb);
> + mutex_unlock(&bdev->bd_fsfreeze_mutex);
> + return 0;
> + }
> +
> if (sb) {
> BUG_ON(sb->s_bdev != bdev);
>
> @@ -244,6 +274,8 @@ void thaw_bdev(struct block_device *bdev
> }
>
> up(&bdev->bd_mount_sem);
> + mutex_unlock(&bdev->bd_fsfreeze_mutex);
> + return 0;

Why do you add a return value here if we always return 0 anyway?