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

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Date:   Tue, 23 May 2023 18:47:39 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     dsterba@...e.cz, Stephen Zhang <starzhangzsd@...il.com>
Cc:     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 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@....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.

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