Re: [RFC PATCH] perf tools: cs-etm: fix endless record after being terminated

[Leo Yan]

Hi Wei,

On Thu, Jan 02, 2020 at 03:41:44PM +0800, Wei Li wrote:
> In __cmd_record(), when receiving SIGINT(ctrl + c), a done flag will
> be set and the event list will be disabled by evlist__disable() once.
> 
> While in auxtrace_record.read_finish(), the related events will be
> enabled again, if they are continuous, the recording seems to be endless.
> 
> If the cs_etm event is disabled, we don't enable it again here.
> 
> Note: This patch is NOT tested since i don't have such a machine with
> coresight feature, but the code seems buggy same as arm-spe and intel-pt.
> 
> Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
> ---
>  tools/perf/arch/arm/util/cs-etm.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index ede040cf82ad..1893a0e3b1e1 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -865,9 +865,13 @@ static int cs_etm_read_finish(struct auxtrace_record *itr, int idx)
>  	struct evsel *evsel;
>  
>  	evlist__for_each_entry(ptr->evlist, evsel) {
> -		if (evsel->core.attr.type == ptr->cs_etm_pmu->type)
> -			return perf_evlist__enable_event_idx(ptr->evlist,
> -							     evsel, idx);
> +		if (evsel->core.attr.type == ptr->cs_etm_pmu->type) {
> +			if (evsel->disabled)
> +				return 0;
> +			else
> +				return perf_evlist__enable_event_idx(
> +						ptr->evlist, evsel, idx);
> +		}
>  	}

I took some time to test on Arm CoreSight, the perf program can be
terminated by Ctrl+c with SIGINT signal on the mainline kernel.

And after capturing ftrace data with below log:

5242      migration/2-19    [002] d..3  4648.383155: sched_migrate_task: comm=perf pid=1692 prio=120 orig_cpu=2 dest_cpu=0
5243      migration/2-19    [002] d..2  4648.383167: sched_switch: prev_comm=migration/2 prev_pid=19 prev_prio=0 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120
5244           <idle>-0     [000] d..2  4648.383167: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=perf next_pid=1692 next_prio=120
5245             perf-1692  [000] d..2  4648.383193: sched_stat_runtime: comm=perf pid=1692 runtime=35420 [ns] vruntime=1636633943 [ns]
5246             perf-1692  [000] d..3  4648.383200: sched_waking: comm=migration/0 pid=11 prio=0 target_cpu=000
5247             perf-1692  [000] dN.4  4648.383203: sched_wakeup: comm=migration/0 pid=11 prio=0 target_cpu=000
5248             perf-1692  [000] dN.2  4648.383205: sched_stat_runtime: comm=perf pid=1692 runtime=9340 [ns] vruntime=1636643283 [ns]
5249             perf-1692  [000] d..2  4648.383208: sched_switch: prev_comm=perf prev_pid=1692 prev_prio=120 prev_state=R+ ==> next_comm=migration/0 next_pid=11 next_prio=0
5250      migration/0-11    [000] d..3  4648.383215: sched_migrate_task: comm=perf pid=1692 prio=120 orig_cpu=0 dest_cpu=1
5251       algorithm1-721   [001] dN.2  4648.383225: sched_stat_runtime: comm=algorithm1 pid=721 runtime=2906000 [ns] vruntime=3501282256244 [ns]
5252       algorithm1-721   [001] d..2  4648.383229: sched_switch: prev_comm=algorithm1 prev_pid=721 prev_prio=120 prev_state=R ==> next_comm=perf next_pid=1692 next_prio=120
5253      migration/0-11    [000] d..2  4648.383235: sched_switch: prev_comm=migration/0 prev_pid=11 prev_prio=0 prev_state=S ==> next_comm=swapper/0 next_pid=0 next_prio=120
5254       algorithm1-721   [001] d..4  4648.383241: <stack trace>
5255  => kprobe_breakpoint_handler
5256  => call_break_hook
5257  => brk_handler
5258  => do_debug_exception
5259  => el1_sync_handler
5260  => el1_sync
5261  => etm_event_stop
5262  => event_sched_out.isra.106
5263  => group_sched_out.part.108
5264  => ctx_sched_out
5265  => task_ctx_sched_out
5266  => __perf_event_task_sched_out
5267  => __schedule
5268  => schedule
5269  => do_notify_resume
5270  => work_pending

We can see after send SIGINT signal, the process 'perf' will be
migrated from CPU2 to CPU0 (line 5242) and it will preempt process
'algorithm1' (line 5252); after the process 'algorithm1' is scheduled
out, the function etm_event_stop() will be invoked to stop tracing.

If we connect with the code in cs_etm_read_finish(), it tries to call
ioctl PERF_EVENT_IOC_ENABLE, but because the process 'algorithm1' is
scheduled out, so the perf event should not be enabled afterwards.

I may miss something at here ... Could you confirm what's the type of
attached process?  normal process or RT process?

Thanks,
Leo

P.s. I tested IntelPT with 5.2-rc3 kernel, it also can be terminated
properly.

>  	return -EINVAL;
> -- 
> 2.17.1
>