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: <20100212204141.cc42f298.akpm@linux-foundation.org>
Date:	Fri, 12 Feb 2010 20:41:41 -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 17:43:39 -0600 Jason Wessel <jason.wessel@...driver.com> wrote:

> >>  	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?
> >
> >   
> 
> I certainly don't want to break kexec or alter any behavior, does that
> mean kgdb / kdb should hook the kexec for notification?
> 
> I think ideally it is a end user's preference as to if they want in via
> kexec or the kernel debugger.  Calling the smp_send_stop() prior to the
> notifier was a death sentence for the kernel debugger. 
> 
> Perhaps I can move the notifier before smp_send_stop()?

Well.  My question can be simplified to "does this break existing code"?
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