linux-kernel - Re: [PATCH linu-next V2] mm/fault: fix comparing pointer to 0

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Message-ID: <87o7vc73cs.fsf@email.froward.int.ebiederm.org>
Date:   Sun, 18 Sep 2022 16:57:23 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     cgel.zte@...il.com
Cc:     richard.henderson@...aro.org, ink@...assic.park.msu.ru,
        mattst88@...il.com, akpm@...ux-foundation.org,
        zhengqi.arch@...edance.com, hannes@...xchg.org,
        catalin.marinas@....com, peterx@...hat.com,
        linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xu Panda <xu.panda@....com.cn>, Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH linu-next V2] mm/fault: fix comparing pointer to 0

cgel.zte@...il.com writes:

> From: Xu Panda <xu.panda@....com.cn>
>
> Do not use assignment in if condition,
> and comparing pointer whith NULL instead of comparing pointer to 0.

Then sensible thing to do if fixup is a pointer value is to just say:

"if (fixup) {"

That will be clearer and not match the pattern you are trying to avoid.

Eric

>
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Xu Panda <xu.panda@....com.cn>
> ---
>  arch/alpha/mm/fault.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
> index ef427a6bdd1a..bb3fe2949313 100644
> --- a/arch/alpha/mm/fault.c
> +++ b/arch/alpha/mm/fault.c
> @@ -194,7 +194,8 @@ do_page_fault(unsigned long address, unsigned long
> mmcsr,
>
>   no_context:
>         /* Are we prepared to handle this fault as an exception?  */
> -       if ((fixup = search_exception_tables(regs->pc)) != 0) {
> +       fixup = search_exception_tables(regs->pc);
> +       if (fixup != NULL) {
>                 unsigned long newpc;
>                 newpc = fixup_exception(dpf_reg, fixup, regs->pc);
>                 regs->pc = newpc;