linux-kernel - Re: [PATCH v2] perf stat: force error in fallback on :k events

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Message-ID: <20200415091836.GH208694@krava>
Date:   Wed, 15 Apr 2020 11:18:36 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2] perf stat: force error in fallback on :k events

On Tue, Apr 14, 2020 at 09:15:50AM -0700, Ian Rogers wrote:

SNIP

> New behavior with paranoid 2:
> $ sudo bash -c "echo 2 > /proc/sys/kernel/perf_event_paranoid"
> $ perf stat -e cycles:k sleep 1
> Error:
> You may not have permission to collect stats.
> 
> Consider tweaking /proc/sys/kernel/perf_event_paranoid,
> which controls use of the performance events system by
> unprivileged users (without CAP_PERFMON or CAP_SYS_ADMIN).
> 
> The current value is 2:
> 
>   -1: Allow use of (almost) all events by all users
>       Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
> >= 0: Disallow ftrace function tracepoint by users without CAP_PERFMON or CAP_SYS_ADMIN
>       Disallow raw tracepoint access by users without CAP_SYS_PERFMON or CAP_SYS_ADMIN
> >= 1: Disallow CPU event access by users without CAP_PERFMON or CAP_SYS_ADMIN
> >= 2: Disallow kernel profiling by users without CAP_PERFMON or CAP_SYS_ADMIN
> 
> To make this setting permanent, edit /etc/sysctl.conf too, e.g.:
> 
>         kernel.perf_event_paranoid = -1
> 
> v2 of this patch addresses the review feedback from jolsa@...hat.com.
> 
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> Reviewed-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/evsel.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index d23db6755f51..b4e8bcb5ab05 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2446,6 +2446,10 @@ bool perf_evsel__fallback(struct evsel *evsel, int err,
>  		char *new_name;
>  		const char *sep = ":";
>  
> +		/* If event has exclude user then don't exclude kernel. */
> +		if (evsel->core.attr.exclude_user)
> +			return false;
> +

nice, it's much simpler

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka

>  		/* Is there already the separator in the name. */
>  		if (strchr(name, '/') ||
>  		    strchr(name, ':'))
> -- 
> 2.26.0.110.g2183baf09c-goog
>