linux-kernel - Re: [PATCH] printk: avoid livelock if another CPU printks continuously

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Message-ID: <20160210112530.04c5512f@gandalf.local.home>
Date:	Wed, 10 Feb 2016 11:25:30 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>, linux-kernel@...r.kernel.org,
	srostedt@...hat.com, Tejun Heo <tj@...nel.org>,
	Peter Hurley <peter@...leysoftware.com>,
	Jan Kara <jack@...e.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kyle McMartin <kyle@...nel.org>,
	KY Srinivasan <kys@...rosoft.com>,
	Dave Jones <davej@...emonkey.org.uk>,
	Calvin Owens <calvinowens@...com>
Subject: Re: [PATCH] printk: avoid livelock if another CPU printks
 continuously

On Wed, 10 Feb 2016 17:10:16 +0100
Petr Mladek <pmladek@...e.com> wrote:

> > Note, it's not that performance critical, and the loop only happens if
> > someone else is adding to the console, which hopefully, should be rare.  
> 
> I probably used too strong words. It is possible that the performance
> impact will not be critical. But the behavior is non-deterministic.
> I think that the approach taken by Jack is more promising.
> I mean the offloading of the console stuff to a workqueue.

My worry about that is that it never comes out. The point about printk,
is that it should pretty much be guaranteed to print. If the system is
dying, and we push it off to a work queue, and that workqueue never
runs, then we lose critical data.

-- Steve