Re: [PATCH] btrfs: use the btrfs_block_group_end() helper everywhere

[Dan Carpenter <dan.carpenter@linaro.org>]

On Mon, Jan 19, 2026 at 06:49:34AM +0000, Johannes Thumshirn wrote:
> On 1/19/26 7:40 AM, Dan Carpenter wrote:
> > d4452bc526c431 Chris Mason     2014-05-19  1202  	u64 start, extent_start, extent_end, len;
> > 7fc5a6968403c7 Filipe Manana   2026-01-16 @1203  	const u64 block_group_end = btrfs_block_group_end(block_group);
> >                                                                                                            ^^^^^^^^^^^^
> > Dereferenced.
> >
> > d4452bc526c431 Chris Mason     2014-05-19  1204  	struct extent_io_tree *unpin = NULL;
> > d4452bc526c431 Chris Mason     2014-05-19  1205  	int ret;
> > 43be21462d8c26 Josef Bacik     2011-04-01  1206
> > 5349d6c3ffead2 Miao Xie        2014-06-19 @1207  	if (!block_group)
> >                                                               ^^^^^^^^^^^
> > Too late.
> 
> I _think_ this check is bogus.
> 
> On one hand  write_pinned_extent_entries() gets called by 
> __btrfs_write_out_cache(), which has the following comment at the top:
> 
> /*
>   * Write out cached info to an inode.
>   *
>   * @inode:       freespace inode we are writing out
>   * @ctl:         free space cache we are going to write out
>   * @block_group: block_group for this cache if it belongs to a block_group
> 
> but then __btrfs_write_out_cache() is only called by 
> btrfs_write_out_cache() which looks like this:
> 
>      ret = __btrfs_write_out_cache(inode, ctl, block_group,
>                        &block_group->io_ctl, trans);
> 
> so iff block_group really is NULL, we'd have a NULL pointer dereference 
> when accessing block_group::io_ctl.
> 
> 
> Same for all the if (block_group) constructs in __btrfs_write_out_cache().
> 

The zero day bot can't use cross function analysis because it doesn't
scale to the number of trees which the bot tests...  Otherwise, sure,
Smatch would silence this warning.

If we remove the NULL check here, should we also remove the NULL checking
in __btrfs_write_out_cache()?  Otherwise there is still a potential that
something will complain about inconsistent NULL checking.

regards,
dan carpenter