linux-kernel - RE: [PATCH] lib/spinlock_debug: avoid one thread can not obtain the spinlock for a long time.

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Message-ID: <FA47D36D6EC9FE4CB463299737C09B9901C14B96@shsmsx102.ccr.corp.intel.com>
Date:	Wed, 30 Apr 2014 06:17:48 +0000
From:	"Wang, Xiaoming" <xiaoming.wang@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Liu, Chuansheng" <chuansheng.liu@...el.com>
Subject: RE: [PATCH] lib/spinlock_debug: avoid one thread can not obtain the
 spinlock for a long time.

Dear Peter
	If we wait the end of loop as loops_per_jiffy. 
It may last more than 130s and local IRQ disabled at interval 
which may cause Hard LOCKUP. We break out in 1 second and
dump the stack for debug.

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Wednesday, April 30, 2014 2:06 PM
> To: Wang, Xiaoming
> Cc: mingo@...hat.com; linux-kernel@...r.kernel.org; Liu, Chuansheng
> Subject: Re: [PATCH] lib/spinlock_debug: avoid one thread can not obtain
> the spinlock for a long time.
> 
> On Wed, Apr 30, 2014 at 01:04:31PM -0400, Wang, Xiaoming wrote:
> > loops_per_jiffy is larger than expectation that possible causes one
> > thread can not obtain the spin lock for a long time.
> > So use cpu_clock() to reach timeout in one second which can avoid
> HARD
> > LOCKUP.
> 
> This is just not making sense.. one thing is broken so then you tape on
> another? Fix the first already.
> 
> Also, why do you care?
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