linux-kernel - [PATCH 3/4] tracing/branch-tracer: Fix a trace recursion on branch tracer

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Date:	Sun, 16 Nov 2008 05:59:52 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/4] tracing/branch-tracer: Fix a trace recursion on branch
 tracer

Impact: Make the branch tracer use raw irq save/restore

When the branch tracer inserts an event through probe_likely_condition(),
it calls local_irq_save() and then results in a trace recursion.

local_irq_save() -> trace_hardirqs_off() -> trace_hardirqs_off_caller()
	-> unlikely()

The trace_branch.c file is protected by DISABLE_BRANCH_PROFILING but that
doesn't prevent from external call to functions that use unlikely().

My box crashed each time I tried to set this tracer (sudden and hard reboot).

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/trace/trace_branch.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index 44bd395..23f9b02 100644
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -41,7 +41,7 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
 	if (unlikely(!tr))
 		return;
 
-	local_irq_save(flags);
+	raw_local_irq_save(flags);
 	cpu = raw_smp_processor_id();
 	if (atomic_inc_return(&tr->data[cpu]->disabled) != 1)
 		goto out;
@@ -73,7 +73,7 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
 
  out:
 	atomic_dec(&tr->data[cpu]->disabled);
-	local_irq_restore(flags);
+	raw_local_irq_restore(flags);
 }
 
 static inline
-- 
1.5.2.5
--
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