From: Martin KaFai Lau <martin.lau@linux.dev>
To: Tonghao Zhang <tong@infragraf.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>, Song Liu <song@kernel.org>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, Hou Tao <houtao1@huawei.com>,
bpf@vger.kernel.org, Manu Bretelle <chantra@meta.com>
Subject: Re: [bpf-next v4 2/2] selftests/bpf: add test case for htab map
Date: Mon, 9 Jan 2023 19:44:11 -0800 [thread overview]
Message-ID: <7a476ec6-9bd0-beec-00ff-e8cd0121ce57@linux.dev> (raw)
In-Reply-To: <85737292-efbf-636c-99f1-39569cd215c8@linux.dev>
On 1/9/23 7:25 PM, Martin KaFai Lau wrote:
>>>
>>> btw, from a quick look at __perf_event_overflow, I suspect doing the
>>> bpf_map_update_elem() here instead of the fentry/perf_event_overflow above
>>> can also reproduce the patch 1 issue?
>> No
>> bpf_overflow_handler will check the bpf_prog_active, if syscall increase it,
>> bpf_overflow_handler will skip the bpf prog.
>
> tbh, I am quite surprised the bpf_prog_active would be noisy enough to avoid
> this deadlock being reproduced easily. fwiw, I just tried doing map_update here
> and can reproduce it in the very first run.
Correcting my self. I only reproduced the warning splat but not the deadlock.
This test is using map_update from the syscall that bumps the prog_active.
Agree that SEC("perf_event") alone won't work unless the bpf_map_update_elem()
is not done from the syscall in prog_tests/htab_deadlock.c, eg. from another bpf
prog.
next prev parent reply other threads:[~2023-01-10 3:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-05 9:26 [bpf-next v4 1/2] bpf: hash map, avoid deadlock with suitable hash mask tong
2023-01-05 9:26 ` [bpf-next v4 2/2] selftests/bpf: add test case for htab map tong
2023-01-05 10:56 ` Hou Tao
2023-01-10 1:33 ` Martin KaFai Lau
2023-01-10 2:21 ` Tonghao Zhang
2023-01-10 3:25 ` Martin KaFai Lau
2023-01-10 3:44 ` Martin KaFai Lau [this message]
2023-01-10 8:10 ` Tonghao Zhang
2023-01-10 1:52 ` [bpf-next v4 1/2] bpf: hash map, avoid deadlock with suitable hash mask Martin KaFai Lau
2023-01-10 2:25 ` Tonghao Zhang
2023-01-10 3:03 ` Martin KaFai Lau
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