linux-kernel - Re: [PATCH] [PING] perf ftrace: Command fails on s390

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Message-ID: <YIMZK3dARqXXsR76@kernel.org>
Date:   Fri, 23 Apr 2021 15:59:55 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Thomas Richter <tmricht@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        svens@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        hca@...ux.ibm.com, Alexander Schmidt <alexschm@...ibm.com>
Subject: Re: [PATCH] [PING] perf ftrace: Command fails on s390

Em Wed, Apr 21, 2021 at 02:04:00PM +0200, Thomas Richter escreveu:
> Command 'perf ftrace -v -- ls' fails in s390 (at least 5.12.0rc6).
> 
> The root cause is a missing pointer dereference which causes an
> array element address to be used as PID.

Since you pinged on this one, and rightly so, please CC:

>From the MAINTAINERS file:

PERFORMANCE EVENTS SUBSYSTEM
R:      Jiri Olsa <jolsa@...hat.com>
R:      Namhyung Kim <namhyung@...nel.org>

These reviewers that help me into getting patches processed.

Patch is processed now, good catch, I collected Namhyung's Acked-by.

Thanks,

- Arnaldo

 
> Fix this by extracting the PID.
> 
> Output before:
>   # ./perf ftrace -v -- ls
>   function_graph tracer is used
>   write '-263732416' to tracing/set_ftrace_pid failed: Invalid argument
>   failed to set ftrace pid
>   #
> 
> Output after:
>    ./perf ftrace -v -- ls
>    function_graph tracer is used
>    # tracer: function_graph
>    #
>    # CPU  DURATION                  FUNCTION CALLS
>    # |     |   |                     |   |   |   |
>    4)               |  rcu_read_lock_sched_held() {
>    4)   0.552 us    |    rcu_lockdep_current_cpu_online();
>    4)   6.124 us    |  }
> 
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> Reported-by: Alexander Schmidt <alexschm@...ibm.com>
> ---
>  tools/perf/builtin-ftrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index d49448a1060c..87cb11a7a3ee 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -289,7 +289,7 @@ static int set_tracing_pid(struct perf_ftrace *ftrace)
>  
>  	for (i = 0; i < perf_thread_map__nr(ftrace->evlist->core.threads); i++) {
>  		scnprintf(buf, sizeof(buf), "%d",
> -			  ftrace->evlist->core.threads->map[i]);
> +			  perf_thread_map__pid(ftrace->evlist->core.threads, i));
>  		if (append_tracing_file("set_ftrace_pid", buf) < 0)
>  			return -1;
>  	}
> -- 
> 2.30.2
> 

-- 

- Arnaldo