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From: Ziyang Men <ziyang.meme@gmail.com>
To: Tejun Heo <tj@kernel.org>
Cc: kernel-team@meta.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>,
	"JP Kobryn" <inwardvessel@gmail.com>,
	"Mykola Lysenko" <mykolal@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 v2 1/2] block: add BPF kfuncs to read blkcg io.stat
Date: Wed, 19 Aug 2026 16:59:55 -0700	[thread overview]
Message-ID: <aoZDe0yvb49flaOs@devvm16600.scu0.facebook.com> (raw)
In-Reply-To: <aoYzjaXQNmm9bDcE@slm.duckdns.org>

Hi Tejun,

On Wed, Aug 19, 2026 at 12:51:57PM -1000, Tejun Heo wrote:
>Hello,
>
>On Wed, Aug 19, 2026 at 03:20:17PM -0700, Ziyang Men wrote:
>> Yes the css_rstat_flush() is exposed but currently it is marked as SLEEPABLE, so
>> it doesn't accept a RCU_PROTECTED css we proposed. This is not a problem for cpu
>> ones since &cgrp->self is a trusted pointer.
>
>Yeah, bummer, so we get ref on cgroups but the subsys pointers are RCU, so
>that means those refs are only RCU protected. I guess we can't avoid a kfunc
>to get acquire a subsys css from cgroup. I wish css_rstat_flush() didn't
>schedule but it does need that cond_resched().

Yeah that would be a pity. I will add kfuncs bpf_cgroup_css() and
bpf_css_release() to handle the reference for the css.

The bpf_blkcg_flush_stats() will be removed as well.

Thanks,
Ziyang

>
>Thanks.
>
>-- 
>tejun

  reply	other threads:[~2026-08-19 23:59 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-08-17 21:42 [PATCH v2 0/2] block: expose blkcg io.stat to BPF Ziyang Men
2026-08-17 21:42 ` [PATCH v2 1/2] block: add BPF kfuncs to read blkcg io.stat Ziyang Men
2026-08-17 22:28   ` bot+bpf-ci
2026-08-18 17:21   ` Tejun Heo
2026-08-18 22:31     ` Ziyang Men
2026-08-18 22:42       ` Tejun Heo
2026-08-18 23:01         ` Ziyang Men
2026-08-19 20:43           ` Tejun Heo
2026-08-19 22:20             ` Ziyang Men
2026-08-19 22:51               ` Tejun Heo
2026-08-19 23:59                 ` Ziyang Men [this message]
2026-08-17 21:42 ` [PATCH v2 2/2] selftests/bpf: add test for blkcg io.stat BPF kfuncs Ziyang Men
2026-08-17 22:41   ` bot+bpf-ci

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