linux-kernel - Re: Re: [PATCH bpf v2] bpf: Fix deadlock when freeing cgroup storage

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Message-ID: <ee5da323-0ad8-4b74-971a-ffbd3eb2b61b@bytedance.com>
Date: Wed, 29 Jan 2025 14:23:42 +0800
From: Abel Wu <wuyun.abel@...edance.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Eduard Zingerman <eddyz87@...il.com>, 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>, David Vernet <void@...ifault.com>,
 "open list:BPF [STORAGE & CGROUPS]" <bpf@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH bpf v2] bpf: Fix deadlock when freeing cgroup storage

On 1/28/25 7:05 AM, Martin KaFai Lau Wrote:
> On 1/27/25 2:15 PM, Alexei Starovoitov wrote:
>> On Sun, Jan 26, 2025 at 1:31 AM Abel Wu <wuyun.abel@...edance.com> wrote:
>>>
>>> On 1/25/25 4:20 AM, Martin KaFai Lau Wrote:
>>>>
>>>> imo, that should be a better option instead of having more unnecessary failures in all other normal use cases which will not be interested in tracing cgroup_storage_ptr().
>>
>> Martin,
>>
>> task_storage_map_free() is doing this busy inc/dec already,
>> in that sense doing the same in cgroup_storage_map_free() fits.
> 
> sgtm. Agree to be consistent with the task_storage_map_free.
> 
> would be nice if the busy inc/dec usage can be revisited after the rqspinlock work.

Agree, and 1ms interval of deadlock dection seems acceptable
for most workloads.

> 
> Acked-by: Martin KaFai Lau <martin.lau@...nel.org>

Thanks Alexei, Martin.