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

[Arnaldo Carvalho de Melo]

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>

?

- 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