linux-kernel - Re: [PATCH] mm: remove the newlines, which are added for unknown reasons and interfere with bug analysis

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Message-ID: <CAO9qdTFwaK36EKV1c8gLCgBG+BR5JmC6=PGk2a6YdHVrH9NukQ@mail.gmail.com>
Date: Mon, 7 Oct 2024 17:57:18 +0900
From: Jeongjun Park <aha310510@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: akpm@...ux-foundation.org, usama.anjum@...labora.com, peterx@...hat.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] mm: remove the newlines, which are added for unknown
 reasons and interfere with bug analysis

Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Mon, Oct 07, 2024 at 03:53:07PM +0900, Jeongjun Park wrote:
> > Looking at the source code links for mm/memory.c in the sample reports
> > in the syzbot report links [1].
> >
> > it looks like the line numbers are designated as lines that have been
> > increased by 1. This may seem like a problem with syzkaller or the
> > addr2line program that assigns the line numbers, but there is no problem
> > with either of them.
> >
> > In the previous commit d61ea1cb0095 ("userfaultfd: UFFD_FEATURE_WP_ASYNC"),
> > when modifying mm/memory.c, an unknown line break is added to the very first
> > line of the file. However, the git.kernel.org site displays the source code
> > with the added line break removed, so even though addr2line has assigned
> > the correct line number, it looks like the line number has increased by 1.
> >
> > This may seem like a trivial thing, but I think it would be appropriate
> > to remove all the newline characters added to the upstream and stable
> > versions, as they are not only incorrect in terms of code style but also
> > hinder bug analysis.
> >
> > [1]
> >
> > https://syzkaller.appspot.com/bug?extid=4145b11cdf925264bff4
> > https://syzkaller.appspot.com/bug?extid=fa43f1b63e3aa6f66329
> > https://syzkaller.appspot.com/bug?extid=890a1df7294175947697
> >
> > Fixes: d61ea1cb0095 ("userfaultfd: UFFD_FEATURE_WP_ASYNC")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Jeongjun Park <aha310510@...il.com>
> > ---
> >  mm/memory.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 2366578015ad..7dffe8749014 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -1,4 +1,3 @@
> > -
>
> This sounds like you have broken tools that can not handle an empty line
> in a file.
>
> Why not fix those?

As I mentioned above, there is no problem with addr2line's ability to parse
the code line that called the function in the calltrace of the crash report.

However, when the source code of mm/memory.c is printed on the screen on the
git.kernel.org site, the line break character that exists in the first line
of the file is deleted and printed, so as a result, all code lines in the
mm/memory.c file are located at line numbers that are -1 less than the
actual line.

You can understand it easily if you compare the source code of mm/memory.c
on github and git.kernel.org.

https://github.com/torvalds/linux/blob/master/mm/memory.c
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/memory.c

Since I cannot modify the source code printing function of the git.kernel.org
site, the best solution I can suggest is to remove the unnecessary line break
character that exists in all versions.

>
> Also, your changelog text has trailing whitespace, ironic for a patch
> that does a whitespace cleanup :)
>

Oops, I forgot to remove the trailing space in the patch description.
If you absolutely must remove the space, I'll write a v2 patch and
send it to you.

Regards,
Jeongjun Park

> thanks,
>
> greg k-h