Re: [PATCH] perf trace: Avoid early exit due SIGCHLD from non-workload processes

[Arnaldo Carvalho de Melo]

On February 9, 2022 3:53:55 PM GMT-03:00, Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>On Wed, Feb 09, 2022 at 12:50:07PM -0300, Arnaldo Carvalho de Melo wrote:
>> Em Wed, Feb 09, 2022 at 04:01:33PM +0100, Jiri Olsa escreveu:
>> > On Tue, Feb 08, 2022 at 10:07:25PM +0800, Changbin Du wrote:
>> > > The function trace__symbols_init() runs "perf-read-vdso32" and that ends up
>> > > with a SIGCHLD delivered to 'perf'. And this SIGCHLD make perf exit early.
>> > > 
>> > > 'perf trace' should exit only if the SIGCHLD is from our workload process.
>> > > So let's use sigaction() instead of signal() to match such condition.
>> > > 
>> > > Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx>
>> > 
>> > good idea, I tested with the reproducer for:
>> >   f06a82f9d31a perf trace: Avoid early exit due to running SIGCHLD handler before it makes sense to
>> > 
>> > and it's working properly
>> > 
>> > Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
>> 
>> So can I replace this with the stronger:
>> 
>> Tested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
>
>I did not see the case described in the changelog,
>just checked the other one was fine..

Ok, I'll keep it as an acked-by then.

- Arnaldo
>
>jirka
>
>> 
>> ?
>> 
>> - Arnaldo
>>  
>> > thanks,
>> > jirka
>> > 
>> > > ---
>> > >  tools/perf/builtin-trace.c | 21 ++++++++++++++++-----
>> > >  1 file changed, 16 insertions(+), 5 deletions(-)
>> > > 
>> > > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
>> > > index 32844d8a0ea5..d03556c14b0a 100644
>> > > --- a/tools/perf/builtin-trace.c
>> > > +++ b/tools/perf/builtin-trace.c
>> > > @@ -1536,13 +1536,20 @@ static size_t trace__fprintf_tstamp(struct trace *trace, u64 tstamp, FILE *fp)
>> > >  	return fprintf(fp, "         ? ");
>> > >  }
>> > >  
>> > > +static pid_t workload_pid = -1;
>> > >  static bool done = false;
>> > >  static bool interrupted = false;
>> > >  
>> > > -static void sig_handler(int sig)
>> > > +static void sighandler_interrupt(int sig __maybe_unused)
>> > >  {
>> > > -	done = true;
>> > > -	interrupted = sig == SIGINT;
>> > > +	done = interrupted = true;
>> > > +}
>> > > +
>> > > +static void sighandler_chld(int sig __maybe_unused, siginfo_t *info,
>> > > +			    void *context __maybe_unused)
>> > > +{
>> > > +	if (info->si_pid == workload_pid)
>> > > +		done = true;
>> > >  }
>> > >  
>> > >  static size_t trace__fprintf_comm_tid(struct trace *trace, struct thread *thread, FILE *fp)
>> > > @@ -3938,7 +3945,6 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
>> > >  	bool draining = false;
>> > >  
>> > >  	trace->live = true;
>> > > -	signal(SIGCHLD, sig_handler);
>> > >  
>> > >  	if (!trace->raw_augmented_syscalls) {
>> > >  		if (trace->trace_syscalls && trace__add_syscall_newtp(trace))
>> > > @@ -4018,6 +4024,7 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
>> > >  			fprintf(trace->output, "Couldn't run the workload!\n");
>> > >  			goto out_delete_evlist;
>> > >  		}
>> > > +		workload_pid = evlist->workload.pid;
>> > >  	}
>> > >  
>> > >  	err = evlist__open(evlist);
>> > > @@ -4887,10 +4894,14 @@ int cmd_trace(int argc, const char **argv)
>> > >  	const char * const trace_subcommands[] = { "record", NULL };
>> > >  	int err = -1;
>> > >  	char bf[BUFSIZ];
>> > > +	struct sigaction sigchld_act = { 0 };
>> > >  
>> > >  	signal(SIGSEGV, sighandler_dump_stack);
>> > >  	signal(SIGFPE, sighandler_dump_stack);
>> > > -	signal(SIGINT, sig_handler);
>> > > +	signal(SIGINT, sighandler_interrupt);
>> > > +	sigchld_act.sa_flags = SA_SIGINFO;
>> > > +	sigchld_act.sa_sigaction = sighandler_chld;
>> > > +	sigaction(SIGCHLD, &sigchld_act, NULL);
>> > >  
>> > >  	trace.evlist = evlist__new();
>> > >  	trace.sctbl = syscalltbl__new();
>> > > -- 
>> > > 2.25.1
>> > > 
>> 
>> -- 
>> 
>> - Arnaldo