From: Steven Rostedt <rostedt@goodmis.org>
Date: Mon, 12 May 2008 19:21:02 +0000 (+0200)
Subject: ftrace: use raw_smp_processor_id for mcount functions
X-Git-Tag: v2.6.27-rc1~1102^2^2~1^2~36
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2bb6f8d6389cbfadd657e7dc069f6986abf35e4f;p=linux-2.6

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@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 40f64f7cd8..af5ad8949a 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -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)