linux-kernel - Re: [perf] perf_event_open() sometimes returning 0

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Date:   Thu, 2 Jan 2020 14:22:47 -0500 (EST)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     linux-kernel@...r.kernel.org
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>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [perf] perf_event_open() sometimes returning 0

On Thu, 2 Jan 2020, Vince Weaver wrote:

> so I was tracking down some odd behavior in the perf_fuzzer which turns 
> out to be because perf_even_open() sometimes returns 0 (indicating a file 
> descriptor of 0) even though as far as I can tell stdin is still open.

error is triggered if aux_sample_size has non-zero value.

seems to be this line in kernel/events/core.c:


 if (perf_need_aux_event(event) && !perf_get_aux_event(event, group_leader))
                goto err_locked;


(note, err is never set)


Vince