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Subject[044/123] tracing: Fix a race in function profile
From: Li Zefan <lizf@cn.fujitsu.com>

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>

---
kernel/trace/ftrace.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -369,11 +369,18 @@ static int function_stat_show(struct seq
{
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;
#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);
@@ -383,17 +390,17 @@ static int function_stat_show(struct seq
avg = rec->time;
do_div(avg, rec->counter);

- mutex_lock(&mutex);
trace_seq_init(&s);
trace_print_graph_duration(rec->time, &s);
trace_seq_puts(&s, " ");
trace_print_graph_duration(avg, &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)



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