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

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Message-ID: <ZzTm7wKsOLuI5w20@mini-arch>
Date: Wed, 13 Nov 2024 09:50:39 -0800
From: Stanislav Fomichev <stfomichev@...il.com>
To: Alexis Lothoré <alexis.lothore@...tlin.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, 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.