linux-kernel - Re: [PATCH] perf stat: Fix endless wait for child process

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Date:   Thu, 3 Jan 2019 12:12:05 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Jin Yao <yao.jin@...ux.intel.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH] perf stat: Fix endless wait for child process

On Thu, Jan 03, 2019 at 03:40:45PM +0800, Jin Yao wrote:
> We hit a perf stat issue by using following script.
> 
>   #!/bin/bash
> 
>   sleep 1000 &
>   exec perf stat -a -e cycles -I1000 -- sleep 5
> 
> Since "perf stat" is launched by exec, so the "sleep 1000" would be
> the child process of "perf stat". The wait4() will not return because
> it's waiting for the child process "sleep 1000" to be end. So perf
> stat doesn't return even 5s passed.
> 
> This patch lets the perf stat return when the specified child process
> is end (in this case, specified child process is "sleep 5").
> 
> Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>

Reviewed-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka

> ---
>  tools/perf/builtin-stat.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 1410d66..63a3afc 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -561,7 +561,8 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>  					break;
>  			}
>  		}
> -		wait4(child_pid, &status, 0, &stat_config.ru_data);
> +		if (child_pid != -1)
> +			wait4(child_pid, &status, 0, &stat_config.ru_data);
>  
>  		if (workload_exec_errno) {
>  			const char *emsg = str_error_r(workload_exec_errno, msg, sizeof(msg));
> -- 
> 2.7.4
>