linux-kernel - Re: [PATCH linux-next] debug:kdb: fix unsigned int win compared to less than zero

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Date:   Fri, 20 Aug 2021 09:46:03 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     jing yangyang <cgel.zte@...il.com>
Cc:     Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Will Deacon <will@...nel.org>,
        Stephen Zhang <stephenzhangzsd@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        LKML <linux-kernel@...r.kernel.org>,
        jing yangyang <jing.yangyang@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH linux-next] debug:kdb: fix unsigned int win compared to
 less than zero

Hi,

On Thu, Aug 19, 2021 at 7:25 PM jing yangyang <cgel.zte@...il.com> wrote:
>
> Fix coccicheck warning:
> ./kernel/debug/kdb/kdb_support.c:575:3-10:
> WARNING:Unsigned expression compared with zero  p_state < 0
>
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: jing yangyang <jing.yangyang@....com.cn>
> ---
>  kernel/debug/kdb/kdb_support.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/debug/kdb/kdb_support.c b/kernel/debug/kdb/kdb_support.c
> index c605b17..fb30801 100644
> --- a/kernel/debug/kdb/kdb_support.c
> +++ b/kernel/debug/kdb/kdb_support.c
> @@ -560,7 +560,7 @@ unsigned long kdb_task_state_string(const char *s)
>   */
>  char kdb_task_state_char (const struct task_struct *p)
>  {
> -       unsigned int p_state;
> +       int p_state;

This was talked about:

https://www.mail-archive.com/kgdb-bugreport@lists.sourceforge.net/msg06159.html

There, Peter Zijlstra said:

> Pre-existing fail that.. but yes that code (and it's carbon copy in
> arch/powerpc/xmon/xmon.c) are clearly bogus and have been for a long
> time afaict.
>
> Ideally someone that cares about this code can replace it with
> get_task_state() or something.

...so while the warning was introduced by commit 2f064a59a11f ("sched:
Change task_struct::state") and your fix papers over of the warning,
it actually doesn't fix the real bug. Apparently the comment
describing the "state" variable before that commit was wrong and "-1"
didn't mean unrunnable.

Maybe you could submit a v2 that does what Peter suggests?

-Doug