linux-kernel - Re: [RFC][PATCH 11/12 v3] printk: Add per_cpu printk func to allow printk to be diverted

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Date:	Thu, 6 Nov 2014 17:56:17 +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>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 11/12 v3] printk: Add per_cpu printk func to allow
 printk to be diverted

On Tue 2014-11-04 10:52:48, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> 
> Being able to divert printk to call another function besides the normal
> logging is useful for such things like NMI handling. If some functions
> are to be called from NMI that does printk() it is possible to lock up
> the box if the nmi handler triggers when another printk is happening.
> 
> One example of this use is to perform a stack trace on all CPUs via NMI.
> But if the NMI is to do the printk() it can cause the system to lock up.
> By allowing the printk to be diverted to another function that can safely
> record the printk output and then print it when it in a safe context
> then NMIs will be safe to call these functions like show_regs().
> 
> Link: http://lkml.kernel.org/p/20140619213952.209176403@goodmis.org
> 
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Looks fine to me.

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

Best Regards,
Petr
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