linux-kernel - Re: [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr

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Date:   Tue, 1 Mar 2022 18:40:04 +0100
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Greg KH <greg@...ah.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christian König <christian.koenig@....com>,
        alsa-devel@...a-project.org, linux-aspeed@...ts.ozlabs.org,
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Subject: Re: [PATCH 2/6] treewide: remove using list iterator after loop body
 as a ptr



> On 1. Mar 2022, at 18:36, Greg KH <greg@...ah.com> wrote:
> 
> On Tue, Mar 01, 2022 at 12:28:15PM +0100, Jakob Koschel wrote:
>> 
>> 
>>> On 1. Mar 2022, at 01:41, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>>> 
>>> On Mon, Feb 28, 2022 at 1:47 PM Jakob Koschel <jakobkoschel@...il.com> wrote:
>>>> 
>>>> The goal of this is to get compiler warnings right? This would indeed be great.
>>> 
>>> Yes, so I don't mind having a one-time patch that has been gathered
>>> using some automated checker tool, but I don't think that works from a
>>> long-term maintenance perspective.
>>> 
>>> So if we have the basic rule being "don't use the loop iterator after
>>> the loop has finished, because it can cause all kinds of subtle
>>> issues", then in _addition_ to fixing the existing code paths that
>>> have this issue, I really would want to (a) get a compiler warning for
>>> future cases and (b) make it not actually _work_ for future cases.
>>> 
>>> Because otherwise it will just happen again.
>>> 
>>>> Changing the list_for_each_entry() macro first will break all of those cases
>>>> (e.g. the ones using 'list_entry_is_head()).
>>> 
>>> So I have no problems with breaking cases that we basically already
>>> have a patch for due to  your automated tool. There were certainly
>>> more than a handful, but it didn't look _too_ bad to just make the
>>> rule be "don't use the iterator after the loop".
>>> 
>>> Of course, that's just based on that patch of yours. Maybe there are a
>>> ton of other cases that your patch didn't change, because they didn't
>>> match your trigger case, so I may just be overly optimistic here.
>> 
>> Based on the coccinelle script there are ~480 cases that need fixing
>> in total. I'll now finish all of them and then split them by
>> submodules as Greg suggested and repost a patch set per submodule.
>> Sounds good?
> 
> Sounds good to me!
> 
> If you need help carving these up and maintaining them over time as
> different subsystem maintainers accept/ignore them, just let me know.
> Doing large patchsets like this can be tough without a lot of
> experience.

Very much appreciated!

There will probably be some cases that do not match one of the pattern
we already discussed and need separate attention.

I was planning to start with one subsystem and adjust the coming ones
according to the feedback gather there instead of posting all of them
in one go.

> 
> thanks,
> 
> greg k-h

- Jakob