linux-kernel - Re: [PATCH] [BUGFIX] x86: mm: fix rcu splat from new TLB tracepoints

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Date:	Thu, 7 Aug 2014 11:11:22 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
	davej@...hat.com, hpa@...or.com, x86@...nel.org
Subject: Re: [PATCH] [BUGFIX] x86: mm: fix rcu splat from new TLB tracepoints

On Thu, Aug 07, 2014 at 10:58:41AM -0700, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> This is a bug fix that needs to be pushed to mainline before the
> 3.17 release.
> 
> Dave Jones reported seeing a bug from one of my TLB tracepoints:
> 
>         http://lkml.kernel.org/r/20140806181801.GA4605@redhat.com
> 
> According to Paul McKenney, the right way to fix this is adding
> an _rcuidle suffix to the tracepoint.
> 
>         http://lkml.kernel.org/r/20140807065055.GA5821@linux.vnet.ibm.com
> 
> This patch does just that.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Reported-by: Dave Jones <davej@...hat.com>,
> Cc: paulmck@...ux.vnet.ibm.com

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> ---
> 
>  b/arch/x86/mm/tlb.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff -puN arch/x86/mm/tlb.c~mm-fix-rcu-splat-from-tlb-tracepoints arch/x86/mm/tlb.c
> --- a/arch/x86/mm/tlb.c~mm-fix-rcu-splat-from-tlb-tracepoints	2014-08-07 10:55:43.312283542 -0700
> +++ b/arch/x86/mm/tlb.c	2014-08-07 10:56:49.763352575 -0700
> @@ -49,7 +49,13 @@ void leave_mm(int cpu)
>  	if (cpumask_test_cpu(cpu, mm_cpumask(active_mm))) {
>  		cpumask_clear_cpu(cpu, mm_cpumask(active_mm));
>  		load_cr3(swapper_pg_dir);
> -		trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
> +		/*
> +		 * This gets called in the idle path where RCU
> +		 * functions differently.  Tracing normally
> +		 * uses RCU, so we have to call the tracepoint
> +		 * specially here.
> +		 */
> +		trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
>  	}
>  }
>  EXPORT_SYMBOL_GPL(leave_mm);
> _
> 

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