Re: [bug report] btrfs: abort transaction in the process_one_buffer() log tree walk callback

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

On Fri, Aug 15, 2025 at 09:28:34AM +0100, Filipe Manana wrote:
> On Fri, Aug 15, 2025 at 7:50 AM Dan Carpenter <dan.carpenter@linaro.org> wrote:
> >
> > Hello Filipe Manana,
> >
> > This is a semi-automatic email about new static checker warnings.
> >
> > Commit f6f79221b128 ("btrfs: abort transaction in the
> > process_one_buffer() log tree walk callback") from Jul 16, 2025,
> > leads to the following Smatch complaint:
> >
> > fs/btrfs/tree-log.c:377 process_one_buffer() warn: variable dereferenced before check 'trans' (see line 375)
> > fs/btrfs/tree-log.c:388 process_one_buffer() warn: variable dereferenced before check 'trans' (see line 375)
> >
> > fs/btrfs/tree-log.c
> >    374          if (wc->pin) {
> >    375                  ret = btrfs_pin_extent_for_log_replay(trans, eb);
> >                                                               ^^^^^
> > The patch adds a dereference
> 
> False alarm. This already happened before that patch, we didn't check
> if wc->trans was NULL before calling
> btrfs_pin_extent_for_log_replay(), and that's fine because if wc->pin
> is true then trans is not NULL.
> 

To be honest, the deleting the NULL check is the most common way to fix
a "pointless NULL check after a dereference" warning...

regards,
dan carpenter