linux-kernel - Re: [PATCH 26/26 v5] x86/nmi: Perform a safe NMI stack trace on all CPUs

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Message-ID: <20141118170258.GM23958@pathway.suse.cz>
Date:	Tue, 18 Nov 2014 18:02:58 +0100
From:	Petr Mladek <pmladek@...e.cz>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 26/26 v5] x86/nmi: Perform a safe NMI stack trace on all
 CPUs

On Fri 2014-11-14 23:59:13, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> 
> When trigger_all_cpu_backtrace() is called on x86, it will trigger an
> NMI on each CPU and call show_regs(). But this can lead to a hard lock
> up if the NMI comes in on another printk().
> 
> In order to avoid this, when the NMI triggers, it switches the printk
> routine for that CPU to call a NMI safe printk function that records the
> printk in a per_cpu seq_buf descriptor. After all NMIs have finished
> recording its data, the seq_bufs are printed in a safe context.
> 
> Link: http://lkml.kernel.org/p/20140619213952.360076309@goodmis.org
> 
> Tested-by: Jiri Kosina <jkosina@...e.cz>
> Acked-by: Jiri Kosina <jkosina@...e.cz>
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Reviewed-by: Petr Mladek <pmladek@...e.cz>

I really like that the NMI part is fast and we do not longer
block many CPUs until the others are finished with priting.

Best Regards,
Petr
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