linux-hardening - Re: [PATCH v2 3/9] crash_core: use panic_try_start() in crash

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Message-ID: <aLEQy-srX89Rndch@debian.debian.local>
Date: Fri, 29 Aug 2025 10:30:35 +0800
From: Qianqiang Liu <qianqiang.liu@....com>
To: Jinchao Wang <wangjinchao600@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>,
	Yury Norov <yury.norov@...il.com>, Simona Vetter <simona@...ll.ch>,
	Helge Deller <deller@....de>, Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	Kees Cook <kees@...nel.org>, Tony Luck <tony.luck@...el.com>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Shixiong Ou <oushixiong@...inos.cn>,
	Zsolt Kajtar <soci@....rulez.org>, Ingo Molnar <mingo@...nel.org>,
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	Joel Granados <joel.granados@...nel.org>,
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	Feng Tang <feng.tang@...ux.alibaba.com>,
	Sravan Kumar Gundu <sravankumarlpu@...il.com>,
	Douglas Anderson <dianders@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Anna Schumaker <anna.schumaker@...cle.com>,
	"Darrick J. Wong" <djwong@...nel.org>,
	Max Kellermann <max.kellermann@...os.com>,
	Yunhui Cui <cuiyunhui@...edance.com>, Tejun Heo <tj@...nel.org>,
	Luo Gengkun <luogengkun@...weicloud.com>,
	Li Huafei <lihuafei1@...wei.com>,
	Thorsten Blum <thorsten.blum@...ux.dev>,
	Yicong Yang <yangyicong@...ilicon.com>, linux-fbdev@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, kexec@...ts.infradead.org,
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/9] crash_core: use panic_try_start() in crash_kexec()

On Mon, Aug 25, 2025 at 10:29:31AM +0800, Jinchao Wang wrote:
> crash_kexec() had its own code to exclude parallel execution by setting
> panic_cpu. This is already handled by panic_try_start(). Switch to
> panic_try_start() to remove the duplication and keep the logic consistent.
> 
> Signed-off-by: Jinchao Wang <wangjinchao600@...il.com>
> ---
>  kernel/crash_core.c | 15 +++------------
>  1 file changed, 3 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index a4ef79591eb2..bb38bbaf3a26 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -4,6 +4,7 @@
>   * Copyright (C) 2002-2004 Eric Biederman  <ebiederm@...ssion.com>
>   */
>  
> +#include "linux/panic.h"

Can you change this line of code to #include <linux/panic.h>?

>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>  
>  #include <linux/buildid.h>
> @@ -143,17 +144,7 @@ STACK_FRAME_NON_STANDARD(__crash_kexec);
>  
>  __bpf_kfunc void crash_kexec(struct pt_regs *regs)
>  {
> -	int old_cpu, this_cpu;
> -
> -	/*
> -	 * Only one CPU is allowed to execute the crash_kexec() code as with
> -	 * panic().  Otherwise parallel calls of panic() and crash_kexec()
> -	 * may stop each other.  To exclude them, we use panic_cpu here too.
> -	 */
> -	old_cpu = PANIC_CPU_INVALID;
> -	this_cpu = raw_smp_processor_id();
> -
> -	if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu)) {
> +	if (panic_try_start()) {
>  		/* This is the 1st CPU which comes here, so go ahead. */
>  		__crash_kexec(regs);
>  
> @@ -161,7 +152,7 @@ __bpf_kfunc void crash_kexec(struct pt_regs *regs)
>  		 * Reset panic_cpu to allow another panic()/crash_kexec()
>  		 * call.
>  		 */
> -		atomic_set(&panic_cpu, PANIC_CPU_INVALID);
> +		panic_reset();
>  	}
>  }
>  
> -- 
> 2.43.0

-- 
Best,
Qianqiang Liu