linux-kernel - [PATCH] tracing/function-return-tracer: Add a barrier to ensure return stack index is incremented in memory

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Date:	Sat, 15 Nov 2008 02:37:44 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: [PATCH] tracing/function-return-tracer: Add a barrier to ensure return
 stack index is incremented in memory

Impact: Fix possible race condition in ftrace function return tracer

This fixes a possible race condition if index incrementation
is not immediately flushed in memory.

Thanks for Andi Kleen and Steven Rostedt for pointing out this issue
and give me this solution.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Andi Kleen <andi@...stfloor.org>
---
 arch/x86/kernel/ftrace.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index fe83273..db25236 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -56,6 +56,7 @@ static int push_return_trace(unsigned long ret, unsigned long long time,
 		return -EBUSY;
 
 	index = ++ti->curr_ret_stack;
+	barrier();
 	ti->ret_stack[index].ret = ret;
 	ti->ret_stack[index].func = func;
 	ti->ret_stack[index].calltime = time;
-- 
1.5.2.5
--
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