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

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Date:   Wed, 9 Feb 2022 19:53:55 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Changbin Du <changbin.du@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf trace: Avoid early exit due SIGCHLD from
 non-workload processes

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@...il.com>
> > 
> > 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@...nel.org>
> 
> So can I replace this with the stronger:
> 
> Tested-by: Jiri Olsa <jolsa@...nel.org>

I did not see the case described in the changelog,
just checked the other one was fine..

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