Re: Bisected KVM hang on x86-32 between v3.12 and v3.13

[Stefan Bader <stefan.bader@canonical.com>]

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On 08.04.2014 14:21, Peter Zijlstra wrote:
> On Mon, Apr 07, 2014 at 08:56:58PM +0200, Peter Zijlstra wrote:
>> On Mon, Apr 07, 2014 at 08:16:24PM +0200, Toralf Förster wrote:
>>
>>> v3.14-10353-g2b3a8fd works fine AFAICS
>>> (BTW the fix is stable material, right ?)
>>
>> I'm fairly sure its not; its a rather invasive series; see:
>>
>> 2432e1364bbe x86: Nuke the supervisor_stack field in i386 thread_info
>> b807902a88c4 x86: Nuke GET_THREAD_INFO_WITH_ESP() macro for i386
>> 0788aa6a23cb x86: Prepare removal of previous_esp from i386 thread_info structure
>> 198d208df437 x86: Keep thread_info on thread stack in x86_32
>>
>> Let me see if there's anything 'simpler' we can stuff in .13+
> 
> OK.. so could someone test the below patch to see if that makes things
> work for .13 and .14?

Hi Peter,

sorry I only had time to try 3.13 but that looks good. I was able to get kvm up
and running for a longer than usual (without the patch) amount of time without
seeing any softlockups.

-Stefan
> 
> ---
>  arch/x86/include/asm/preempt.h | 11 +++++++++++
>  include/linux/preempt.h        |  4 ++++
>  include/linux/thread_info.h    |  2 --
>  3 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
> index c8b051933b1b..7ada46d8d4d8 100644
> --- a/arch/x86/include/asm/preempt.h
> +++ b/arch/x86/include/asm/preempt.h
> @@ -5,6 +5,17 @@
>  #include <asm/percpu.h>
>  #include <linux/thread_info.h>
>  
> +#ifdef CONFIG_X86_32
> +/*
> + * i386's current_thread_info() depends on ESP and for interrupt/exception
> + * stacks this doesn't yield the actual task thread_info.
> + *
> + * We hard rely on the fact that all the TIF_NEED_RESCHED bits are
> + * the same, therefore use the slightly more expensive version below.
> + */
> +#define tif_need_resched() test_tsk_thread_flag(current, TIF_NEED_RESCHED)
> +#endif
> +
>  DECLARE_PER_CPU(int, __preempt_count);
>  
>  /*
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index de83b4eb1642..891c8f8b52fe 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -17,6 +17,10 @@
>  
>  #include <asm/preempt.h>
>  
> +#ifndef tif_need_resched
> +#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED)
> +#endif
> +
>  #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
>  extern void preempt_count_add(int val);
>  extern void preempt_count_sub(int val);
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index fddbe2023a5d..a629e4b23217 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -118,8 +118,6 @@ static inline __deprecated void set_need_resched(void)
>  	 */
>  }
>  
> -#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED)
> -
>  #if defined TIF_RESTORE_SIGMASK && !defined HAVE_SET_RESTORE_SIGMASK
>  /*
>   * An arch can define its own version of set_restore_sigmask() to get the
> 



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