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SubjectRe: [PATCH] perf: correctly handle failed perf_get_aux_event() (was: Re: [perf] perf_event_open() sometimes returning 0)
On Mon, 6 Jan 2020, Mark Rutland wrote:

> On Thu, Jan 02, 2020 at 02:22:47PM -0500, Vince Weaver wrote:
> > On Thu, 2 Jan 2020, Vince Weaver wrote:
> >
> Vince, does the below (untested) patch work for you?


yes, this patch fixes things for me.

Tested-by: Vince Weaver <vincent.weaver@maine.edu>



> ---->8----
> From c79f31b42aaf85f3a924af9218794b3bc8b79892 Mon Sep 17 00:00:00 2001
> From: Mark Rutland <mark.rutland@arm.com>
> Date: Mon, 6 Jan 2020 11:51:06 +0000
> Subject: [PATCH] perf: correctly handle failed perf_get_aux_event()
>
> Vince reports a worrying issue:
>
> | 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.
>
> ... and further the cause:
>
> | 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)
>
> This seems to be a thinko in commit:
>
> ab43762ef010967e ("perf: Allow normal events to output AUX data")
>
> ... and we should probably return -EINVAL here, as this should only
> happen when the new event is mis-configured or does not have a
> compatible aux_event group leader.
>
> Fixes: ab43762ef010967e ("perf: Allow normal events to output AUX data")
> Reported-by: Vince Weaver <vincent.weaver@maine.edu>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> ---
> kernel/events/core.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index a1f8bde19b56..2173c23c25b4 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -11465,8 +11465,10 @@ SYSCALL_DEFINE5(perf_event_open,
> }
> }
>
> - if (perf_need_aux_event(event) && !perf_get_aux_event(event, group_leader))
> + if (perf_need_aux_event(event) && !perf_get_aux_event(event, group_leader)) {
> + err = -EINVAL;
> goto err_locked;
> + }
>
> /*
> * Must be under the same ctx::mutex as perf_install_in_context(),
> --
> 2.11.0
>
>

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