linux-kernel - Re: [RFC][PATCH 3/3] x86/nmi: Perform a safe NMI stack trace on all CPUs

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Message-ID: <alpine.LNX.2.00.1411191143520.4454@pobox.suse.cz>
Date:	Wed, 19 Nov 2014 11:44:56 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Borislav Petkov <bp@...en8.de>
cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Petr Mladek <pmladek@...e.cz>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andy Lutomirski <luto@...capital.net>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [RFC][PATCH 3/3] x86/nmi: Perform a safe NMI stack trace on all
 CPUs

On Wed, 19 Nov 2014, Borislav Petkov wrote:

> I'm wondering if this could be used in a generic manner throughout code 
> where we could say "ok, I'm in an NMI context, so lemme switch printk's 
> and do some printing" so that NMI and NMI-like atomic contexts could use 
> printk. Lemme do an mce example:
> 
> do_machine_check(..)
> {
> 	printk_func_t printk_func_save = this_cpu_read(printk_func);
> 
> 	...
> 
> 	/* in #MC handler, switch printks */
> 	this_cpu_write(printk_func, nmi_vprintk);
> 
> 	printk("This is a hw error, details: ...\n");
> 
> 	/* more bla */
> 
> 	this_cpu_write(printk_func, printk_func_save);
> }
> 
> or should we change that in entry.S, before we call the handler?

If we are going down this path, do_nmi() should be early enough to do it, 
no need to pollute NMI assembly code with this.

-- 
Jiri Kosina
SUSE Labs
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