[PATCH] [BUGFIX] x86: mm: fix rcu splat from new TLB tracepoints

[PATCH] [BUGFIX] x86: mm: fix rcu splat from new TLB tracepoints

[Dave Hansen]

From: Dave Hansen <dave.hansen@linux.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@linux.intel.com>
Reported-by: Dave Jones <davej@redhat.com>,
Cc: paulmck@linux.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);
_

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

[Paul E. McKenney]

On Thu, Aug 07, 2014 at 10:58:41AM -0700, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@linux.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@linux.intel.com>
> Reported-by: Dave Jones <davej@redhat.com>,
> Cc: paulmck@linux.vnet.ibm.com

Reviewed-by: Paul E. McKenney <paulmck@linux.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);
> _
> 

[tip:x86/urgent] x86/mm: Fix RCU splat from new TLB tracepoints

[tip-bot for Dave Hansen]

Commit-ID:  7c7f1547b627092737493f0781780af85cc9b1a4
Gitweb:     http://git.kernel.org/tip/7c7f1547b627092737493f0781780af85cc9b1a4
Author:     Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate: Thu, 7 Aug 2014 10:58:41 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 8 Aug 2014 10:35:00 +0200

x86/mm: Fix RCU splat from new TLB tracepoints

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.

Reported-by: Dave Jones <davej@redhat.com>,
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140807175841.5C92D878@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/mm/tlb.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 1fe3398..98b7976 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -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);