Received-SPF: pass (google.com: domain of linux-kernel+bounces-117178-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
References: <000000000000dc9aca0613ec855c@google.com>
 <tencent_F436364A347489774B677A3D13367E968E09@qq.com>
 <CAADnVQJQvcZOA_BbFxPqNyRbMdKTBSMnf=cKvW7NJ8LxxP54sA@mail.gmail.com>
 <87y1a6biie.fsf@cloudflare.com>
User-agent: mu4e 1.6.10; emacs 29.2
From: Jakub Sitnicki <jakub@cloudflare.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>, Edward Adam Davis
 <eadavis@qq.com>, John Fastabend <john.fastabend@gmail.com>
Cc: syzbot+c4f4d25859c2e5859988@syzkaller.appspotmail.com,
 42.hyeyoo@gmail.com, andrii@kernel.org, ast@kernel.org,
 bpf@vger.kernel.org, daniel@iogearbox.net, davem@davemloft.net,
 edumazet@google.com, kafai@fb.com, kpsingh@kernel.org, kuba@kernel.org,
 linux-kernel@vger.kernel.org, namhyung@kernel.org, netdev@vger.kernel.org,
 pabeni@redhat.com, peterz@infradead.org, songliubraving@fb.com,
 syzkaller-bugs@googlegroups.com, yhs@fb.com
Subject: Re: [PATCH] bpf, sockmap: fix deadlock in rcu_report_exp_cpu_mult
Date: Mon, 25 Mar 2024 14:49:19 +0100
In-reply-to: <87y1a6biie.fsf@cloudflare.com>
Message-ID: <87ttkuber7.fsf@cloudflare.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain

On Mon, Mar 25, 2024 at 01:23 PM +01, Jakub Sitnicki wrote:

[...]

> But we also need to cover sock_map_unref->sock_sock_map_del_link called
> from sock_hash_delete_elem. It also grabs a spin lock.

On second look, no need to disable interrupts in
sock_map_unref->sock_sock_map_del_link. Call is enclosed in the critical
section in sock_hash_delete_elem that has been updated.

I have a question, though, why are we patching sock_hash_free? It
doesn't get called unless there are no more existing users of the BPF
map. So nothing can mutate it from interrupt context.

[...]