[PATCH] perf trace: Fix race in signal handling

[PATCH] perf trace: Fix race in signal handling

[Michael Petlan]

Since a lot of stuff happens before the SIGINT signal handler is registered
(scanning /proc/*, etc.), on bigger systems, such as Cavium Sabre CN99xx,
it may happen that first interrupt signal is lost and perf isn't correctly
terminated.

The reproduction code might look like the following:

    perf trace -a &
    PERF_PID=$!
    sleep 4
    kill -INT $PERF_PID

The issue has been found on a CN99xx machine with RHEL-8 and the patch fixes
it by registering the signal handlers earlier in the init stage.

Suggested-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Michael Petlan <mpetlan@redhat.com>
Tested-by: Michael Petlan <mpetlan@redhat.com>
---
 tools/perf/builtin-trace.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 85b6a46e85b6..7ec18ff57fc4 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -3964,9 +3964,6 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
 
 	evlist__config(evlist, &trace->opts, &callchain_param);
 
-	signal(SIGCHLD, sig_handler);
-	signal(SIGINT, sig_handler);
-
 	if (forks) {
 		err = evlist__prepare_workload(evlist, &trace->opts.target, argv, false, NULL);
 		if (err < 0) {
@@ -4827,6 +4824,8 @@ int cmd_trace(int argc, const char **argv)
 
 	signal(SIGSEGV, sighandler_dump_stack);
 	signal(SIGFPE, sighandler_dump_stack);
+	signal(SIGCHLD, sig_handler);
+	signal(SIGINT, sig_handler);
 
 	trace.evlist = evlist__new();
 	trace.sctbl = syscalltbl__new();
-- 
2.18.4

Re: [PATCH] perf trace: Fix race in signal handling

[Arnaldo Carvalho de Melo]

Em Tue, Mar 02, 2021 at 03:41:20PM +0100, Michael Petlan escreveu:
> Since a lot of stuff happens before the SIGINT signal handler is registered
> (scanning /proc/*, etc.), on bigger systems, such as Cavium Sabre CN99xx,
> it may happen that first interrupt signal is lost and perf isn't correctly
> terminated.
> 
> The reproduction code might look like the following:
> 
>     perf trace -a &
>     PERF_PID=$!
>     sleep 4
>     kill -INT $PERF_PID
> 
> The issue has been found on a CN99xx machine with RHEL-8 and the patch fixes
> it by registering the signal handlers earlier in the init stage.

Thanks, applied.

- Arnaldo

 
> Suggested-by: Jiri Olsa <jolsa@redhat.com>
> Signed-off-by: Michael Petlan <mpetlan@redhat.com>
> Tested-by: Michael Petlan <mpetlan@redhat.com>
> ---
>  tools/perf/builtin-trace.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 85b6a46e85b6..7ec18ff57fc4 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -3964,9 +3964,6 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
>  
>  	evlist__config(evlist, &trace->opts, &callchain_param);
>  
> -	signal(SIGCHLD, sig_handler);
> -	signal(SIGINT, sig_handler);
> -
>  	if (forks) {
>  		err = evlist__prepare_workload(evlist, &trace->opts.target, argv, false, NULL);
>  		if (err < 0) {
> @@ -4827,6 +4824,8 @@ int cmd_trace(int argc, const char **argv)
>  
>  	signal(SIGSEGV, sighandler_dump_stack);
>  	signal(SIGFPE, sighandler_dump_stack);
> +	signal(SIGCHLD, sig_handler);
> +	signal(SIGINT, sig_handler);
>  
>  	trace.evlist = evlist__new();
>  	trace.sctbl = syscalltbl__new();
> -- 
> 2.18.4
> 

-- 

- Arnaldo