linux-kernel - Re: [PATCH 0/2] printk vs rq->lock and xtime lock

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Message-ID: <alpine.LFD.1.00.0803241021350.17905@woody.linux-foundation.org>
Date:	Mon, 24 Mar 2008 10:58:50 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] printk vs rq->lock and xtime lock



On Mon, 24 Mar 2008, Peter Zijlstra wrote:
> 
> As to the regression reported by Marcin; what happens is that we invoke
> printk() while holding the xtime lock for writing. printk() will call
> wake_up_klogd() which tries to enqueue klogd on some rq.
> 
> The known deadlock here is calling printk() while holding rq->lock, which
> would then try to recusively lock the rq again when trying to wake klogd.

Ok.

Right now, however, I think that for 2.6.25 I'll just remove the printk. 

And for the long haul, I really don't think the solution is 
"printk_nowakup()", because this is going to happen again when somebody 
doesn't realize the code is called with the rq lock held, and it's going 
to be a bitch to debug.

I just don't think this is maintainable. 

		Linus
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