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From: JP Kobryn <jp.kobryn@linux.dev>
To: Tejun Heo <tj@kernel.org>
Cc: "Ziyang Men" <ziyang.meme@gmail.com>,
	"Jens Axboe" <axboe@kernel.dk>,
	"Josef Bacik" <josef@toxicpanda.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Eduard Zingerman" <eddyz87@gmail.com>,
	"Kumar Kartikeya Dwivedi" <memxor@gmail.com>,
	"Martin KaFai Lau" <martin.lau@linux.dev>,
	"Song Liu" <song@kernel.org>,
	"Yonghong Song" <yonghong.song@linux.dev>,
	"Jiri Olsa" <jolsa@kernel.org>,
	"Emil Tsalapatis" <emil@etsalapatis.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Michal Koutný" <mkoutny@suse.com>,
	"Roman Gushchin" <roman.gushchin@linux.dev>,
	"Shakeel Butt" <shakeel.butt@linux.dev>,
	"Mykola Lysenko" <mykolal@meta.com>,
	kernel-team@meta.com, linux-block@vger.kernel.org,
	bpf@vger.kernel.org, cgroups@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] block: add BPF kfuncs to read blkcg io.stat
Date: Tue, 11 Aug 2026 15:07:15 -0700	[thread overview]
Message-ID: <c9fe7691-d808-4363-a826-14ac8a9bd575@linux.dev> (raw)
In-Reply-To: <antT1wtJEZ02CDx1@slm.duckdns.org>

On 8/11/26 9:54 AM, Tejun Heo wrote:
> Hello,
> 
> On Mon, Aug 10, 2026 at 05:17:26PM -0700, JP Kobryn wrote:
> ...
>> The get/put kfuncs above use KF_ACQUIRE/RELEASE so the verifier can
>> reject memcg access after the put. Replacing them with a generic API
>> would call for tracking a new lifetime relationship between the css and
>> memcg (or other derived) pointer.
> 
> So, if you need css -> memcg casting, I think that can just be RCU
> protected. In fact, even for the iteration and access, RCU protection
> probably makes more sense then KF_ACQUIRE/RELEASE. It's simpler and less
> overhead especially given that most bpf progs that people care about are
> non-sleepable and already in RCU critical section anyway.
> 
It's just that if flushing is involved, the cond_resched() within
css_rstat_flush() would preclude RCU.

  reply	other threads:[~2026-08-11 22:07 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-08-07 19:37 [PATCH 0/2] block: expose blkcg io.stat to BPF Ziyang Men
2026-08-07 19:37 ` [PATCH 1/2] block: add BPF kfuncs to read blkcg io.stat Ziyang Men
2026-08-07 20:00   ` sashiko-bot
2026-08-10 20:00   ` Tejun Heo
2026-08-10 22:46     ` Ziyang Men
2026-08-11  0:17       ` JP Kobryn
2026-08-11 16:54         ` Tejun Heo
2026-08-11 22:07           ` JP Kobryn [this message]
2026-08-12  1:07     ` Shakeel Butt
2026-08-07 19:37 ` [PATCH 2/2] selftests/bpf: add test for blkcg io.stat BPF kfuncs Ziyang Men
2026-08-07 19:51   ` sashiko-bot

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