linux-kernel - RE: [PATCH] Fix rq->lock vs logbuf

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Message-ID: <E807E903FE6CBE4D95E420FBFCC273B827522A@nasanexd01h.na.qualcomm.com>
Date:	Wed, 20 Feb 2013 09:38:28 +0000
From:	"Bu, Yitian" <ybu@....qualcomm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...nel.org" <mingo@...nel.org>
Subject: RE: [PATCH] Fix rq->lock vs logbuf_lock unlock race



> -----Original Message-----
> From: Peter Zijlstra [mailto:a.p.zijlstra@...llo.nl]
> Sent: Wednesday, February 20, 2013 4:45 PM
> To: Bu, Yitian
> Cc: tglx@...utronix.de; linux-kernel@...r.kernel.org; mingo@...nel.org
> Subject: Re: [PATCH] Fix rq->lock vs logbuf_lock unlock race
> 
> On Mon, 2013-02-18 at 12:53 +0000, Bu, Yitian wrote:
> > This patch is for kernel V3.7.9
> >
> > From 8796f4a2175a323aaa49ea8dd0fe68678dd5dccd Mon Sep 17 00:00:00
> 2001
> > From: ybu <ybu@....qualcomm.com>
> > Date: Mon, 18 Feb 2013 19:52:01 +0800
> > Subject: [PATCH] Fix rq->lock vs logbuf_lock unlock race
> >
> > fix up the fallout from commit 07354eb1a74d1 ("locking printk:
> > Annotate logbuf_lock as raw")
> > Release console_sem after unlocking the logbuf_lock avoids some lock
> > inversion troubles between logbuf_lock and rq->lock.
> 
> Please clarify how and where.. you're not actually supposed to use
> printk() while holding rq->lock.
> 

1. the patch 0b5e1c5255e, which is written by you,  release console_sem
after logbuf_lock. But the patch 07354eb1a revert one of your change, it 
reintroduced a lock inversion problem which was fixed in 0b5e1c5255.
The purpose of my patch is the same as your patch 0b5e1c5255e.

2. from printk comment: "This is printk(). It can be called from any context. 
We want it to work. ". I suppose to use printk in any context.