From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Song Liu <songliubraving@fb.com>
Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
netdev@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
kernel-team@fb.com, john.fastabend@gmail.com,
kpsingh@chromium.org, brouer@redhat.com, peterz@infradead.org
Subject: Re: [PATCH v4 bpf-next 2/4] bpf: fail PERF_EVENT_IOC_SET_BPF when bpf_get_[stack|stackid] cannot work
Date: Wed, 22 Jul 2020 22:55:18 -0700 [thread overview]
Message-ID: <20200723055518.onydx7uhmzomt7ud@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20200722184210.4078256-3-songliubraving@fb.com>
On Wed, Jul 22, 2020 at 11:42:08AM -0700, Song Liu wrote:
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 856d98c36f562..f77d009fcce95 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9544,6 +9544,24 @@ static int perf_event_set_bpf_handler(struct perf_event *event, u32 prog_fd)
> if (IS_ERR(prog))
> return PTR_ERR(prog);
>
> + if (event->attr.precise_ip &&
> + prog->call_get_stack &&
> + (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY) ||
> + event->attr.exclude_callchain_kernel ||
> + event->attr.exclude_callchain_user)) {
> + /*
> + * On perf_event with precise_ip, calling bpf_get_stack()
> + * may trigger unwinder warnings and occasional crashes.
> + * bpf_get_[stack|stackid] works around this issue by using
> + * callchain attached to perf_sample_data. If the
> + * perf_event does not full (kernel and user) callchain
> + * attached to perf_sample_data, do not allow attaching BPF
> + * program that calls bpf_get_[stack|stackid].
> + */
> + bpf_prog_put(prog);
> + return -EINVAL;
I suspect this will be a common error. bpftrace and others will be hitting
this issue and would need to fix how they do perf_event_open.
But EINVAL is too ambiguous and sys_perf_event_open has no ability to
return a string.
So how about we pick some different errno here to make future debugging
a bit less painful?
May be EBADFD or EPROTO or EPROTOTYPE ?
I think anything would be better than EINVAL.
next prev parent reply other threads:[~2020-07-23 5:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-22 18:42 [PATCH v4 bpf-next 0/4] bpf: fix stackmap on perf_events with PEBS Song Liu
2020-07-22 18:42 ` [PATCH v4 bpf-next 1/4] bpf: separate bpf_get_[stack|stackid] for perf events BPF Song Liu
2020-07-22 18:42 ` [PATCH v4 bpf-next 2/4] bpf: fail PERF_EVENT_IOC_SET_BPF when bpf_get_[stack|stackid] cannot work Song Liu
2020-07-23 5:55 ` Alexei Starovoitov [this message]
2020-07-23 6:20 ` Song Liu
2020-07-23 15:22 ` Alexei Starovoitov
2020-07-22 18:42 ` [PATCH v4 bpf-next 4/4] selftests/bpf: add get_stackid_cannot_attach Song Liu
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