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

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Message-ID: <Yh5ZmwiH5AxtQ69K@kroah.com>
Date:   Tue, 1 Mar 2022 18:36:27 +0100
From:   Greg KH <greg@...ah.com>
To:     Jakob Koschel <jakobkoschel@...il.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 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.

thanks,

greg k-h