linux-kernel - Re: [PATCH bpf-next 07/10] selftests/bpf: migrate flow

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Message-ID: <2fefeddf-c426-4a3f-90ae-64e01fc7a557@bootlin.com>
Date: Thu, 14 Nov 2024 08:58:21 +0100
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman
 <eddyz87@...il.com>, Mykola Lysenko <mykolal@...com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>,
 ebpf@...uxfoundation.org, Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Bastien Curutchet <bastien.curutchet@...tlin.com>,
 Petar Penkov <ppenkov@...gle.com>, bpf@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 07/10] selftests/bpf: migrate flow_dissector
 namespace exclusivity test

On 11/13/24 18:50, Stanislav Fomichev wrote:
> On 11/13, Alexis Lothoré wrote:
>> On 11/13/24 14:53, Alexis Lothoré (eBPF Foundation) wrote:
>>
>> [...]
>>
>>> +	ns = open_netns(TEST_NS);
>>> +	bpf_prog_detach2(prog_fd, 0, BPF_FLOW_DISSECTOR);
>>> +	close_netns(ns);
>>
>> I would like to mention that I initially planned to directly delete the
>> namespace to perform the test cleanup, assuming it would be enough to consider
>> any non-root namespace flow_dissector to be removed. However I observed that it
>> made other tests dealing with flow_dissector starting to fail with -EEXIST,
>> despite all those tests being marked as "serial". I started examining this,
>> suspecting a real issue (a race between namespace deletion and flow dissector
>> attachment check, or a ns refcount issue) but before going further: is my
>> assumption right ? Should a mere namespace deletion be indeed enough to remove
>> the corresponding bpf flow dissector ? Or am I missing something ? If so I'll
>> keep examining this.
> 
> Don't think that's expected. Removing a namespace with an attached
> dissector program should (in theory) clearly detach it.

ACK, thanks, I'll keep investigating this then.

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com