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Commit 3aaba20f authored by Li Zefan's avatar Li Zefan Committed by Steven Rostedt
Browse files

tracing: Fix a race in function profile 



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: default avatarLi Zefan <lizf@cn.fujitsu.com>
Cc: stable@kernel.org
LKML-Reference: <4C723644.4040708@cn.fujitsu.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent fa66f07a

kernel/trace/ftrace.c

+11 −4
Original line number Diff line number Diff line
@@ -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)