Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log_inode

[Qu Wenruo]

On 2023/5/23 05:51, David Sterba wrote:
> On Wed, May 17, 2023 at 05:07:55PM +0800, Stephen Zhang wrote:
> > Qu Wenruo <quwenruo.btrfs@xxxxxxx> 于2023年5月17日周三 15:47写道：
> > > On 2023/5/16 09:34, zhangshida wrote:
> > > > From: Shida Zhang <zhangshida@xxxxxxxxxx>
> > > >
> > > > This fixes the following warning reported by gcc 10 under x86_64:
> > >
> > > Full gcc version please.
> >
> > it's "gcc (Debian 10.2.1-6) 10.2.1 20210110".
> >
> > > Especially you need to check if your gcc10 is the latest release.
> > >
> > > If newer gcc (12.2.1) tested without such error, it may very possible to
> > > be a false alert.
> > >
> > > And in fact it is.
> > >
> > > @first_dir_index would only be assigned to @last_range_start if
> > > last_range_end != 0.
> > >
> > > Thus the loop must have to be executed once, and @last_range_start won't
> > > be zero.
> >
> > Yup, I know it's a false positive. What I don't know is the criterion
> > that decides whether it is a good patch.
>
> If you have analyzed the code and found out that it was indeed a false
> positive then please state that in the changelog. Fixing it still makes
> sense so the compiler version and briefly explaining why you fix it that
> way makes it a good patch.
>
> > That is,
> > it doesn't look so good because it is a false alert and the latest gcc
> > can get rid of such warnings, based on what you said( if I understand
> > correctly).
> > Or,
> > It looks okay because the patch can make some older gcc get a cleaner
> > build and do no harm to the original code logic.
>
> In general I agree here.
>
> > In fact, I've seen Linus complaining about the warning generated by
> > some gcc version in another thread.
> >
> > https://lore.kernel.org/linux-xfs/168384265493.22863.2683852857659893778.pr-tracker-bot@xxxxxxxxxx/T/#t
>
> I share the POV for warning fixes, I'd rather see new reports after
> fixing the previous ones than reminding everybody to update.

Or can we only enable -Wmaybe-uninitialized only for certain builds?
Like binding it with CONFIG_BTRFS_DEBUG?

So far all warning are false alerts, and I'm really not a fan of false
alerts.

The -Wmaybe-uninitialized option doesn't look that reliable on older
compilers, and for developers we're more or less using uptodate
toolchains anyway.

Thanks,
Qu