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: Li Zefan <lizf@cn.fujitsu.com>
Cc: stable@kernel.org
LKML-Reference: <4C723644.4040708@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 0d88ce9..7cb1f45 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -381,12 +381,19 @@
{
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 @@
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 @@
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)