From: Li Zefan <lizf@cn.fujitsu.com>
Date: Mon, 23 Aug 2010 08:50:12 +0000 (+0800)
Subject: tracing: Fix a race in function profile
X-Git-Tag: v2.6.35.5~56
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=b8536db269735d35d2b9a6480d40de212fed1b3c;p=karo-tx-linux.git

tracing: Fix a race in function profile

commit 3aaba20f26f58843e8f20611e5c0b1c06954310f upstream.

While we are reading trace_stat/functionX and someone just
disabled function_profile at that time, we can trigger this:

	divide error: 0000 [#1] PREEMPT SMP
	...
	EIP is at function_stat_show+0x90/0x230
	...

This fix just takes the ftrace_profile_lock and checks if
rec->counter is 0. If it's 0, we know the profile buffer
has been reset.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4C723644.4040708@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 6d2cb14f9449..83836650e54b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -381,12 +381,19 @@ static int function_stat_show(struct seq_file *m, void *v)
 {
 	struct ftrace_profile *rec = v;
 	char str[KSYM_SYMBOL_LEN];
+	int ret = 0;
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	static DEFINE_MUTEX(mutex);
 	static struct trace_seq s;
 	unsigned long long avg;
 	unsigned long long stddev;
 #endif
+	mutex_lock(&ftrace_profile_lock);
+
+	/* we raced with function_profile_reset() */
+	if (unlikely(rec->counter == 0)) {
+		ret = -EBUSY;
+		goto out;
+	}
 
 	kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
 	seq_printf(m, "  %-30.30s  %10lu", str, rec->counter);
@@ -408,7 +415,6 @@ static int function_stat_show(struct seq_file *m, void *v)
 		do_div(stddev, (rec->counter - 1) * 1000);
 	}
 
-	mutex_lock(&mutex);
 	trace_seq_init(&s);
 	trace_print_graph_duration(rec->time, &s);
 	trace_seq_puts(&s, "    ");
@@ -416,11 +422,12 @@ static int function_stat_show(struct seq_file *m, void *v)
 	trace_seq_puts(&s, "    ");
 	trace_print_graph_duration(stddev, &s);
 	trace_print_seq(m, &s);
-	mutex_unlock(&mutex);
 #endif
 	seq_putc(m, '\n');
+out:
+	mutex_unlock(&ftrace_profile_lock);
 
-	return 0;
+	return ret;
 }
 
 static void ftrace_profile_reset(struct ftrace_profile_stat *stat)