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

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Message-ID: <aKXQ96ZE6yyfUuYq@MiWiFi-R3L-srv>
Date: Wed, 20 Aug 2025 21:43:19 +0800
From: Baoquan He <bhe@...hat.com>
To: Jinchao Wang <wangjinchao600@...il.com>
Cc: pmladek@...e.com, akpm@...ux-foundation.org,
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	linux-kernel@...r.kernel.org, feng.tang@...ux.alibaba.com,
	joel.granados@...nel.org, john.ogness@...utronix.de,
	namcao@...utronix.de, sravankumarlpu@...il.com,
	kexec@...ts.infradead.org
Subject: Re: [PATCH 3/9] crash_core: use panic_try_start() in crash_kexec()

On 08/20/25 at 09:35pm, Baoquan He wrote:
> On 08/20/25 at 05:14pm, 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"
> >  #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()) {
> 
> Seriously, where can I find this panic_try_start() and the
> panic_reset()? 

Ok, just found it's in a patch series. Grabbed the patchset and will
have a look.

> 
> >  		/* 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
> > 
>