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

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Date:	Fri, 8 Aug 2014 02:19:21 -0700
From:	tip-bot for Dave Hansen <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	torvalds@...ux-foundation.org, dave@...1.net,
	paulmck@...ux.vnet.ibm.com, tglx@...utronix.de,
	dave.hansen@...ux.intel.com
Subject: [tip:x86/urgent] x86/mm: Fix RCU splat from new TLB tracepoints

Commit-ID:  7c7f1547b627092737493f0781780af85cc9b1a4
Gitweb:     http://git.kernel.org/tip/7c7f1547b627092737493f0781780af85cc9b1a4
Author:     Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate: Thu, 7 Aug 2014 10:58:41 -0700
Committer:  Ingo Molnar <mingo@...nel.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@...hat.com>,
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Dave Hansen <dave@...1.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/20140807175841.5C92D878@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.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);
--
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