From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8125642A96; Wed, 19 Aug 2026 22:51:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787179919; cv=none; b=rqvenZYseu/GJP24YTv2yVM5MZNYfjMpZmP6XrPpvlo5HrEzE+ft24zshR9CAZ2qJqnvMUepk2ssS/r+1W9KViIErlUCQyq69HEEyq4UoLrB32XvFsj9hVdL5mpqybqz752Gid+witYeZHlgDUfzxzUkWbCwyO0MsexJogE2Iek= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787179919; c=relaxed/simple; bh=a8znbGTtU25MC0b1skPIq2SPK/UcXJV63+Tidewo3pQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FwbSjUwaz7DgpTmc45UmTosWtEiRaHLy7q85aH9jzmwJ7Pac/l/e1fmk+GcCjO1/c8CO2JJyitQVj7i4ybHDLANRwK8C/YWsKpv93s21y62yvV+VRuDp6q18tQlTWqRhICp/1WmPfiUxwxmtWwuINK2Y5P4arLzdpQhNYxNDdbk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=II0+Fkqu; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="II0+Fkqu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F191E1F000E9; Wed, 19 Aug 2026 22:51:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787179918; bh=S2bKynL2yXaKWbSw85s0IvCAlaumC+saXxJ1IubC7yg=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=II0+Fkquu7LRsweGUQSuyJTgMVQZ6C3z/+Q3jxlVSMVJKxXYFt5y0kZkM8v1lEhMn J6bRUUE4+Q863+EoJjMwB+s2BNHElGRUFazo3kJ69ZPDullD72ViYWNcAaF2fKCo0P Q6jInjg1ctRseROA+C/EW+l+gqm+tA1iorlaN7S0XMVAFnF/WZF6Aie21fqA5NqXDX GpK3xSKBzf3402DgMYeDhkMRW5dNOzMzqzMMfvdw+sppEqU5geSflTS9uLbn2pRHGD VyclfYq834A9SXqbyFu2YrbywNVjHqvTMaiwQYjnK3X86qY+m4fCrfXijpG4bNtET0 5dpJsybUli/hg== Date: Wed, 19 Aug 2026 12:51:57 -1000 From: Tejun Heo To: Ziyang Men Cc: kernel-team@meta.com, Jens Axboe , Josef Bacik , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Shuah Khan , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Roman Gushchin , Shakeel Butt , JP Kobryn , Mykola Lysenko , 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 Message-ID: References: <20260817214205.723267-1-ziyang.meme@gmail.com> <20260817214205.723267-2-ziyang.meme@gmail.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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(). Thanks. -- tejun