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Date:   Wed, 19 Jan 2022 08:15:10 +0100
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Yuntao Wang <ytcoode@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Remove redundant assignment to variable ret

On Wed, Jan 19, 2022 at 5:18 AM Yuntao Wang <ytcoode@...il.com> wrote:
>
> On Mon, Jan 17, 2022 at 3:47 PM Lukas Bulwahn <lukas.bulwahn@...il.com> wrote:
> > Dear Yuntao,
> >
> >
> > when you consider removing dead-store assignments guided by some static
> > analyzer, you need to check if the code you are looking at is actually
> > missing an error-handling branch.
> >
> > In this case, ftrace_process_locs() may return -ENOMEM, and the caller
> > needs to appropriately deal with this error return code. Your patch
> > does not change the code at all, i.e., the compiled object code is the
> > same as after the patch as before.
> >
> > Think about how to deal appropriately with the -ENOMEM return in this
> > caller and submit a patch that implements the right error-handling
> > branch or argue in your commit message why that is not needed at all.
> >
> > If you do not understand or cannot check such basic code properties for
> > dead-store assignments, it might be better to work on some other aspect
> > and area of the kernel repository. E.g., the kernel documentation build
> > also has a few warnings that deserve patches to be fixed.
> >
> >
> > Best regards,
> >
> > Lukas
>
> Dear Lukas,
>
> Thanks for your reply.
>
> Actually, I had read the source code carefully and noticed the possible
> error return code -ENOMEM of the ftrace_process_locs() function.
>
> At first I was going to implement an error-handling branch as you said,
> but after digging into more details, I discovered:
>
> - The ftrace_init() function did not handle the error return code of the ftrace_process_locs() function since the first version.
> - The ftrace_module_init() function did not handle it either.
>

This is certainly important information on the rationale, and hence,
this needs to go into the commit message explaining why you propose
this change.

Now, you should also explain: why do you consider it not a problem
that this error situation -ENOMEM is not handled by the caller?

And if so, why should ftrace_process_locs() even return an error code
if this error return is not considered?

Your commit message should really explain this reasoning.

> To keep consistent with the existing code, I just removed the assignment
> in that patch.
>
> Maybe we should deal with the error return code more appropriately,
> at least print some warnings?
>

This might be one way of dealing with it.

Lukas

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