Re: [PATCH 07/12] fs: stop using get_super in fs_mark_dead

Jan Kara
2023-08-03T13:14:24Z

On Wed 02-08-23 17:41:26, Christoph Hellwig wrote:
> fs_mark_dead currently uses get_super to find the superblock for the
> block device that is going away. This means it is limited to the
> main device stored in sb->s_dev, leading to a lot of code duplication
> for file systems that can use multiple block devices.
>
> Now that the holder for all block devices used by file systems is set
> to the super_block, we can instead look at that holder and then check
> if the file system is born and active, so do that instead.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/super.c | 30 ++++++++++++++++++++++++++----
> 1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/fs/super.c b/fs/super.c
> index 09b65ee1a8b737..0cda4af0a7e16c 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1209,17 +1209,39 @@ int get_tree_keyed(struct fs_context *fc,
> EXPORT_SYMBOL(get_tree_keyed);
>
> #ifdef CONFIG_BLOCK
> +/*
> + * Lock a super block that the callers holds a reference to.
> + *
> + * The caller needs to ensure that the super_block isn't being freed while
> + * calling this function, e.g. by holding a lock over the call to this function
> + * and the place that clears the pointer to the superblock used by this function
> + * before freeing the superblock.
> + */
> +static bool lock_active_super(struct super_block *sb)
> +{
> + down_read(&sb->s_umount);
> + if (!sb->s_root ||
> + (sb->s_flags & (SB_ACTIVE | SB_BORN)) != (SB_ACTIVE | SB_BORN)) {
> + up_read(&sb->s_umount);
> + return false;
> + }
> + return true;
> +}
> +
> static void fs_mark_dead(struct block_device *bdev)
> {
> - struct super_block *sb;
> + struct super_block *sb = bdev->bd_holder;
>
> - sb = get_super(bdev);
> - if (!sb)
> + /* bd_holder_lock ensures that the sb isn't freed */
> + lockdep_assert_held(&bdev->bd_holder_lock);
> +
> + if (!lock_active_super(sb))
> return;
>
> if (sb->s_op->shutdown)
> sb->s_op->shutdown(sb);
> - drop_super(sb);
> +
> + up_read(&sb->s_umount);
> }
>
> static const struct blk_holder_ops fs_holder_ops = {
> --
> 2.39.2
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR