linux-kernel - Re: [PATCH 26/28] kdb,panic,debug_core: Allow the debug core to receive a panic before smp_send

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Message-Id: <20100212150027.f875bbde.akpm@linux-foundation.org>
Date:	Fri, 12 Feb 2010 15:00:27 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jason Wessel <jason.wessel@...driver.com>
Cc:	linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
	mingo@...e.hu
Subject: Re: [PATCH 26/28] kdb,panic,debug_core: Allow the debug core to
 receive a panic before smp_send_stop()

On Fri, 12 Feb 2010 16:35:41 -0600 Jason Wessel <jason.wessel@...driver.com> wrote:

> It is highly desirable to trap into kdb on panic,

s/kdb/kgdb/

But is it necessary to do it in-kernel?  Why not just put a
breakpoint at panic(), add that to your .gdbinit?

> diff --git a/kernel/panic.c b/kernel/panic.c
> index c787333..428d15b 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -66,10 +66,13 @@ NORET_TYPE void panic(const char * fmt, ...)
>  	 */
>  	preempt_disable();
>  
> -	bust_spinlocks(1);
>  	va_start(args, fmt);
>  	vsnprintf(buf, sizeof(buf), fmt, args);
>  	va_end(args);
> +
> +	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
> +
> +	bust_spinlocks(1);
>  	printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);
>  #ifdef CONFIG_DEBUG_BUGVERBOSE
>  	dump_stack();
> @@ -91,8 +94,6 @@ NORET_TYPE void panic(const char * fmt, ...)
>  	 */
>  	smp_send_stop();
>  
> -	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
> -
>  	bust_spinlocks(0);
>  
>  	if (!panic_blink)

So the notifier call now happens before all the printks and the kexec
and kmsg_dump handling.  What effect does this have upon the code which
implements kexec and kmsg_dump?

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