Hi Jiri,
Sorry for late reply. I've been busy these days.
On Thu, 25 Apr 2013 15:24:18 +0900, Namhyung Kim wrote:
> On Wed, 24 Apr 2013 16:12:41 +0200, Jiri Olsa wrote:
>> I got following lockup for record command:
>>
>> # ./perf --no-pager ftrace record ls
>> ...
>> hangs
>>
>> in other terminal:
>>
>> # pstack 14237
>> Thread 2 (Thread 0x7f3f1aa1d700 (LWP 14241)):
>> #0 0x0000003cec20b595 in pthread_cond_wait@@GLIBC_2.3.2 () from
>> /lib64/libpthread.so.0
>> #1 0x0000000000446ebe in record_ftrace_raw_buffer (arg=0x21f9ce0) at
>> builtin-ftrace.c:451
>> #2 0x0000003cec207d14 in start_thread () from /lib64/libpthread.so.0
>> #3 0x0000003cebaf168d in clone () from /lib64/libc.so.6
>> Thread 1 (Thread 0x7f3f1ba209c0 (LWP 14237)):
>> #0 0x0000003cec208e60 in pthread_join () from /lib64/libpthread.so.0
>> #1 0x0000000000449c8c in do_ftrace_record
>> (ftrace=ftrace@entry=0x7fff1377d240) at builtin-ftrace.c:682
>> #2 0x000000000044a57b in __cmd_ftrace_record (argv=0x7fff1377d818,
>> argc=<optimized out>, ftrace=0x7fff1377d240) at builtin-ftrace.c:1535
>> #3 cmd_ftrace (argc=2, argv=0x7fff1377d818, prefix=<optimized out>) at
>> builtin-ftrace.c:1655
>> #4 0x000000000041a763 in run_builtin (p=p@entry=0x7d58a0,
>> argc=argc@entry=3, argv=argv@entry=0x7fff1377d818) at perf.c:320
>> #5 0x0000000000419faf in handle_internal_command (argv=0x7fff1377d818,
>> argc=3) at perf.c:377
>> #6 run_argv (argv=0x7fff1377d600, argcp=0x7fff1377d60c) at perf.c:421
>> #7 main (argc=3, argv=0x7fff1377d818) at perf.c:522
>>
>
> How often can you reproduce it? I can't. :(
>
> But it looks there's a race between cond_wait() and cond_broatcast().
> I'll take a look at that.
I think the problem is that a recorder can be blocked if it received a
broadcast signal before calling cond_wait(). So I modified the code to
place signaling ready_cond and waiting start_cond in the same cs.
Does the patch below fix your problem?
Thanks,
Namhyung
diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 4296948197de..f1ecfa207822 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -428,12 +428,6 @@ static void *record_ftrace_raw_buffer(void *arg)
fra->state = RECORD_STATE__READY;
- /* Now I'm ready */
- pthread_mutex_lock(&recorder_mutex);
- recorder_count++;
- pthread_cond_signal(&recorder_ready_cond);
- pthread_mutex_unlock(&recorder_mutex);
-
/*
* block all signals but SIGUSR2.
* It'll be used to unblock a recorder to finish.
@@ -447,7 +441,10 @@ static void *record_ftrace_raw_buffer(void *arg)
fcntl(trace_fd, F_SETFL, O_NONBLOCK);
pollfd.fd = trace_fd;
+ /* Now I'm ready */
pthread_mutex_lock(&recorder_mutex);
+ recorder_count++;
+ pthread_cond_signal(&recorder_ready_cond);
pthread_cond_wait(&recorder_start_cond, &recorder_mutex);
pthread_mutex_unlock(&recorder_mutex);
--
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