linux-kernel - Re: [PATCH] printk: robustify printk

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Message-Id: <1219236181.8651.46.camel@twins>
Date:	Wed, 20 Aug 2008 14:43:01 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>, tglx@...utronix.de,
	marcin.slusarz@...il.com, linux-kernel@...r.kernel.org,
	davem@...emloft.net, rostedt@...dmis.org,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH] printk: robustify printk

On Wed, 2008-08-20 at 14:40 +0200, Jiri Kosina wrote:
> On Mon, 11 Aug 2008, Ingo Molnar wrote:
> 
> > ----------------->
> > >From b845b517b5e3706a3729f6ea83b88ab85f0725b0 Mon Sep 17 00:00:00 2001
> > From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Date: Fri, 8 Aug 2008 21:47:09 +0200
> > Subject: [PATCH] printk: robustify printk
> > 
> > Avoid deadlocks against rq->lock and xtime_lock by deferring the klogd
> > wakeup by polling from the timer tick.
> > 
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> Then I think we also want the patch below on top of that, right?

Indeed, Thanks!

> 
> From: Jiri Kosina <jkosina@...e.cz>
> printk: robustify printk, fix #3
> 
> Remove the comment describing the possibility of printk() deadlocking on 
> runqueue lock.
> 
> Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> --- 
> 
>  kernel/printk.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/printk.c b/kernel/printk.c
> index b51b156..9fbf391 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -577,9 +577,6 @@ static int have_callable_console(void)
>   * @fmt: format string
>   *
>   * This is printk().  It can be called from any context.  We want it to work.
> - * Be aware of the fact that if oops_in_progress is not set, we might try to
> - * wake klogd up which could deadlock on runqueue lock if printk() is called
> - * from scheduler code.
>   *
>   * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
>   * call the console drivers.  If we fail to get the semaphore we place the output

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