linux-kernel - Re: [PATCH v2 1/9] perf evsel: Always preserve errno while cleaning up perf_event

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Date:   Tue, 22 Oct 2019 10:01:00 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     acme@...nel.org, linux-kernel@...r.kernel.org, jolsa@...nel.org,
        eranian@...gle.com, kan.liang@...ux.intel.com,
        peterz@...radead.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v2 1/9] perf evsel: Always preserve errno while cleaning
 up perf_event_open failures

On Sun, Oct 20, 2019 at 10:51:54AM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> In some cases when perf_event_open fails, it may do some closes to clean
> up. In special cases these closes can fail too, which overwrites the
> errno of the perf_event_open, which is then incorrectly reported.
> 
> Save/restore errno around closes.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>

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

thanks,
jirka

> ---
>  tools/perf/util/evsel.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index abc7fda4a0fe..d831038b55f2 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1574,7 +1574,7 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
>  {
>  	int cpu, thread, nthreads;
>  	unsigned long flags = PERF_FLAG_FD_CLOEXEC;
> -	int pid = -1, err;
> +	int pid = -1, err, old_errno;
>  	enum { NO_CHANGE, SET_TO_MAX, INCREASED_MAX } set_rlimit = NO_CHANGE;
>  
>  	if ((perf_missing_features.write_backward && evsel->core.attr.write_backward) ||
> @@ -1727,8 +1727,8 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
>  	 */
>  	if (err == -EMFILE && set_rlimit < INCREASED_MAX) {
>  		struct rlimit l;
> -		int old_errno = errno;
>  
> +		old_errno = errno;
>  		if (getrlimit(RLIMIT_NOFILE, &l) == 0) {
>  			if (set_rlimit == NO_CHANGE)
>  				l.rlim_cur = l.rlim_max;
> @@ -1812,6 +1812,7 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
>  	if (err)
>  		threads->err_thread = thread;
>  
> +	old_errno = errno;
>  	do {
>  		while (--thread >= 0) {
>  			close(FD(evsel, cpu, thread));
> @@ -1819,6 +1820,7 @@ int evsel__open(struct evsel *evsel, struct perf_cpu_map *cpus,
>  		}
>  		thread = nthreads;
>  	} while (--cpu >= 0);
> +	errno = old_errno;
>  	return err;
>  }
>  
> -- 
> 2.21.0
>