Re: [bug report] btrfs: extent_io: do extra check for extent buffer read write functions

[David Sterba <dsterba@suse.cz>]

On Fri, Sep 15, 2023 at 10:10:13AM +0300, Dan Carpenter wrote:
> Hello Qu Wenruo,
> 
> The patch f98b6215d7d1: "btrfs: extent_io: do extra check for extent
> buffer read write functions" from Aug 19, 2020 (linux-next), leads to
> the following Smatch static checker warning:
> 
> fs/btrfs/print-tree.c:186 print_uuid_item() error: uninitialized symbol 'subvol_id'.
> fs/btrfs/tests/extent-io-tests.c:338 check_eb_bitmap() error: uninitialized symbol 'has'.
> fs/btrfs/tests/extent-io-tests.c:353 check_eb_bitmap() error: uninitialized symbol 'has'.
> fs/btrfs/uuid-tree.c:203 btrfs_uuid_tree_remove() error: uninitialized symbol 'read_subid'.
> fs/btrfs/uuid-tree.c:353 btrfs_uuid_tree_iterate() error: uninitialized symbol 'subid_le'.
> fs/btrfs/uuid-tree.c:72 btrfs_uuid_tree_lookup() error: uninitialized symbol 'data'.
> fs/btrfs/volumes.c:7415 btrfs_dev_stats_value() error: uninitialized symbol 'val'.
> 
> fs/btrfs/extent_io.c
>   4096  void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
>   4097                          unsigned long start, unsigned long len)
>   4098  {
>   4099          void *eb_addr = btrfs_get_eb_addr(eb);
>   4100  
>   4101          if (check_eb_range(eb, start, len))
>   4102                  return;
>                         ^^^^^^^
> 
> Originally this used to memset dstv to zero but now it just returns.
> I can easily just mark that error path as impossible.  These days
> everyone with a brain zeros their stack variables anyway so it shouldn't
> affect anyone who doesn't deserve it.

Thanks, this explains the other errors reported on linux-next with
possibly uninitialized variables.