linux-kernel - [PATCH] ftrace: use raw_smp_processor

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Message-ID: <Pine.LNX.4.58.0804231639490.28387@gandalf.stny.rr.com>
Date:	Wed, 23 Apr 2008 16:41:17 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] ftrace: use raw_smp_processor_id for mcount functions


Due to debug hooks in the kernel that can change the way smp_processor_id
works, use raw_smp_processor_id in mcount called functions (namely
ftrace_record_ip). Currently we annotate most debug functions from calling
mcount, but we should not rely on that to prevent kernel lockups.

This patch uses the raw_smp_processor_id to prevent a recusive crash
that can happen if a debug hook in smp_processor_id calls mcount.

Signed-off-by: Steven Rostedt <srostedt@...hat.com>
---
 kernel/trace/ftrace.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

Index: linux-sched-devel.git/kernel/trace/ftrace.c
===================================================================
--- linux-sched-devel.git.orig/kernel/trace/ftrace.c	2008-04-09 11:47:32.000000000 -0400
+++ linux-sched-devel.git/kernel/trace/ftrace.c	2008-04-23 16:39:05.000000000 -0400
@@ -267,6 +267,7 @@ ftrace_record_ip(unsigned long ip)
 	unsigned long key;
 	int resched;
 	int atomic;
+	int cpu;

 	if (!ftrace_enabled || ftrace_disabled)
 		return;
@@ -274,9 +275,15 @@ ftrace_record_ip(unsigned long ip)
 	resched = need_resched();
 	preempt_disable_notrace();

-	/* We simply need to protect against recursion */
-	__get_cpu_var(ftrace_shutdown_disable_cpu)++;
-	if (__get_cpu_var(ftrace_shutdown_disable_cpu) != 1)
+	/*
+	 * We simply need to protect against recursion.
+	 * Use the the raw version of smp_processor_id and not
+	 * __get_cpu_var which can call debug hooks that can
+	 * cause a recursive crash here.
+	 */
+	cpu = raw_smp_processor_id();
+	per_cpu(ftrace_shutdown_disable_cpu, cpu)++;
+	if (per_cpu(ftrace_shutdown_disable_cpu, cpu) != 1)
 		goto out;

 	if (unlikely(ftrace_record_suspend))
@@ -317,7 +324,7 @@ ftrace_record_ip(unsigned long ip)
  out_unlock:
 	spin_unlock_irqrestore(&ftrace_shutdown_lock, flags);
  out:
-	__get_cpu_var(ftrace_shutdown_disable_cpu)--;
+	per_cpu(ftrace_shutdown_disable_cpu, cpu)--;

 	/* prevent recursion with scheduler */
 	if (resched)

--
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