linux-kernel - Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log

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Date:   Mon, 22 May 2023 23:51:44 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Stephen Zhang <starzhangzsd@...il.com>
Cc:     Qu Wenruo <quwenruo.btrfs@....com>, clm@...com,
        josef@...icpanda.com, dsterba@...e.com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhangshida@...inos.cn, k2ci <kernel-bot@...inos.cn>
Subject: Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log_inode

On Wed, May 17, 2023 at 05:07:55PM +0800, Stephen Zhang wrote:
> Qu Wenruo <quwenruo.btrfs@....com> 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@...inos.cn>
> > >
> > > 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@kernel.org/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.