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Date:	Thu, 3 Apr 2014 14:07:58 -0700
From:	David Cohen <david.a.cohen@...ux.intel.com>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, mingo@...nel.org, gnomes@...rguk.ukuu.org.uk,
	hpa@...or.com
Subject: Re: Soft lockup regression since kernel 3.13

On Thu, Apr 03, 2014 at 12:11:03PM -0700, David Cohen wrote:
> On Wed, Apr 02, 2014 at 04:29:48PM -0700, David Cohen wrote:
> > Hi,
> > 
> > I've detected a regression from upstream (using an Intel Merrifield
> > device) since 3.13 (still exists in 3.14) which I never had much time
> > to start to investigate until now. The symptoms are: the device boots
> > and works fine for while until it silently hangs.
> > 
> > I finally bisected v3.12..v3.13 and found exactly which commit created
> > the issue:
> > 
> > commit f27dde8deef33c9e58027df11ceab2198601d6a6
> > Author: Peter Zijlstra <peterz@...radead.org>
> > Date:   Wed Aug 14 14:55:31 2013 +0200
> > 
> >     sched: Add NEED_RESCHED to the preempt_count
> 
> FWIW I did further investigation and made the issue to go away with this
> hack:

And using the attached .config.

Br, David

> 
> diff --git a/arch/x86/include/asm/preempt.h
> b/arch/x86/include/asm/preempt.h
> index c8b051933b1b..41744d99c88f 100644
> --- a/arch/x86/include/asm/preempt.h
> +++ b/arch/x86/include/asm/preempt.h
> @@ -95,7 +95,7 @@ static __always_inline bool
> __preempt_count_dec_and_test(void)
>   */
>    static __always_inline bool should_resched(void)
>     {
>     -       return unlikely(!__this_cpu_read_4(__preempt_count));
>     +       return unlikely(tif_need_resched());
>      }
>       
>        #ifdef CONFIG_PREEMPT
> --
> 
> I extended part of this patch to x86:
> 
> commit ba1f14fbe70965ae0fb1655a5275a62723f65b77
> Author: Peter Zijlstra <peterz@...radead.org>
> Date:   Thu Nov 28 14:26:41 2013 +0100
> 
>     sched: Remove PREEMPT_NEED_RESCHED from generic code
> --
> 
> Br, David Cohen

View attachment ".config" of type "text/plain" (93009 bytes)

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