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

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Date:	Thu, 07 Aug 2014 10:58:41 -0700
From:	Dave Hansen <dave@...1.net>
To:	linux-kernel@...r.kernel.org
Cc:	Dave Hansen <dave@...1.net>, dave.hansen@...ux.intel.com,
	davej@...hat.com, paulmck@...ux.vnet.ibm.com, hpa@...or.com,
	x86@...nel.org
Subject: [PATCH] [BUGFIX] x86: mm: fix rcu splat from new TLB tracepoints


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
---

 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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