On Mon 07-01-13 20:41:04, Fernando Luis Vázquez Cao wrote:
> Using get_active_super will not work properly if the fs (like btrfs) does not
> save its s_bdev with the device it is on. Also it does not provide the entire
> picture, since an filesystem can be contained on multiple disks (again like
> btrfs).
>
> Fortunately we now have a bd_super field in struct block_device were a pointer
> to the superblock sitting on top of the block device can be stored.
>
> Filesystems using the vfs helper mount_bdev (the ext filesystems, xfs, etc) and
> gfs2 already do this (for the former it is a freebie), so for these there is
> no need to iterate through the list of superblocks; we can get the superblock
> directly from ->bd_super which is more efficient and what this patch
> implements.
>
> A multi-device filesystem (once again lile btrfs) can use that field to store
> a pointer to the superblock for each block device in its storage pool. By
> doing so it would get_active_super and, by extension, thaw_bdev initiated
> freezes working.
>
> Thanks go to Josef Bacik and Christoph Hellwig for initiating this effort
> to fix btrfs and for suggesting the solution implemented here, respectively.
Looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: linux-btrfs@xxxxxxxxxxxxxxx
> Cc: Josef Bacik <jbacik@xxxxxxxxxxxx>
> Cc: Eric Sandeen <sandeen@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
> Cc: Chris Mason <chris.mason@xxxxxxxxxxxx>
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx>
> ---
>
> diff -urNp linux-3.8-rc1-orig/fs/super.c linux-3.8-rc1/fs/super.c
> --- linux-3.8-rc1-orig/fs/super.c 2012-12-25 16:35:43.100018000 +0900
> +++ linux-3.8-rc1/fs/super.c 2012-12-25 16:36:22.312018000 +0900
> @@ -632,26 +632,29 @@ struct super_block *get_super(struct blo
> return NULL;
>
> spin_lock(&sb_lock);
> + if ((sb = bdev->bd_super) != NULL)
> + goto out_found;
> rescan:
> list_for_each_entry(sb, &super_blocks, s_list) {
> if (hlist_unhashed(&sb->s_instances))
> continue;
> - if (sb->s_bdev == bdev) {
> - sb->s_count++;
> - spin_unlock(&sb_lock);
> - down_read(&sb->s_umount);
> - /* still alive? */
> - if (sb->s_root && (sb->s_flags & MS_BORN))
> - return sb;
> - up_read(&sb->s_umount);
> - /* nope, got unmounted */
> - spin_lock(&sb_lock);
> - __put_super(sb);
> - goto rescan;
> - }
> + if (sb->s_bdev == bdev)
> + goto out_found;
> }
> spin_unlock(&sb_lock);
> return NULL;
> +out_found:
> + sb->s_count++;
> + spin_unlock(&sb_lock);
> + down_read(&sb->s_umount);
> + /* still alive? */
> + if (sb->s_root && (sb->s_flags & MS_BORN))
> + return sb;
> + up_read(&sb->s_umount);
> + /* nope, got unmounted */
> + spin_lock(&sb_lock);
> + __put_super(sb);
> + goto rescan;
> }
>
> EXPORT_SYMBOL(get_super);
> @@ -696,18 +699,22 @@ struct super_block *get_active_super(str
>
> restart:
> spin_lock(&sb_lock);
> + if ((sb = bdev->bd_super) != NULL)
> + goto out_grabsuper;
> list_for_each_entry(sb, &super_blocks, s_list) {
> if (hlist_unhashed(&sb->s_instances))
> continue;
> - if (sb->s_bdev == bdev) {
> - if (grab_super(sb)) /* drops sb_lock */
> - return sb;
> - else
> - goto restart;
> - }
> + if (sb->s_bdev == bdev)
> + goto out_grabsuper;
> }
> spin_unlock(&sb_lock);
> return NULL;
> +
> +out_grabsuper:
> + if (grab_super(sb)) /* drops sb_lock */
> + return sb;
> + else
> + goto restart;
> }
>
> struct super_block *user_get_super(dev_t dev)
>
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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