Re: [PATCH v2] btrfs: tree-checker: Fix wrong check on max devid

[Anand Jain <anand.jain@oracle.com>]

On 27/8/19 10:05 PM, Qu Wenruo wrote:
> Btrfs doesn't reuse devid, thus if we add and delete device in a loop,
> we can increase devid to higher value, triggering tree checker to give a
> false alert.
> 
> Furthermore, we have dev extent verification already (after
> tree-checker, at mount time).
> So even if user had bitflip on some dev items, we can still detect it
> and refuse to mount.
> 
> Reported-by: Anand Jain <anand.jain@oracle.com>
> Fixes: ab4ba2e13346 ("btrfs: tree-checker: Verify dev item")
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> Changelog:
> v2:
> - Remove devid check completely
>    As we already have verify_one_dev_extent().
> ---
>   fs/btrfs/tree-checker.c | 8 --------
>   1 file changed, 8 deletions(-)
> 
> diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
> index 43e488f5d063..076d5b8014fb 100644
> --- a/fs/btrfs/tree-checker.c
> +++ b/fs/btrfs/tree-checker.c
> @@ -686,9 +686,7 @@ static void dev_item_err(const struct extent_buffer *eb, int slot,
>   static int check_dev_item(struct extent_buffer *leaf,
>   			  struct btrfs_key *key, int slot)
>   {
> -	struct btrfs_fs_info *fs_info = leaf->fs_info;
>   	struct btrfs_dev_item *ditem;
> -	u64 max_devid = max(BTRFS_MAX_DEVS(fs_info), BTRFS_MAX_DEVS_SYS_CHUNK);
>   
>   	if (key->objectid != BTRFS_DEV_ITEMS_OBJECTID) {
>   		dev_item_err(leaf, slot,
> @@ -696,12 +694,6 @@ static int check_dev_item(struct extent_buffer *leaf,
>   			     key->objectid, BTRFS_DEV_ITEMS_OBJECTID);
>   		return -EUCLEAN;
>   	}
> -	if (key->offset > max_devid) {
> -		dev_item_err(leaf, slot,
> -			     "invalid devid: has=%llu expect=[0, %llu]",
> -			     key->offset, max_devid);
> -		return -EUCLEAN;
> -	}
>   	ditem = btrfs_item_ptr(leaf, slot, struct btrfs_dev_item);
>   	if (btrfs_device_id(leaf, ditem) != key->offset) {
>   		dev_item_err(leaf, slot,
> 

   Though ab4ba2e13346 didn't add BTRFS_MAX_DEVS_SYS_CHUNK,
   BTRFS_MAX_DEVS_SYS_CHUNK is unused now, can be deleted.

   The reproducer script and logs should rather be in this change log.

Thanks, Anand