From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 E4D94332EBB; Fri, 14 Aug 2026 06:45:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786689948; cv=none; b=gPYJovRKO4ruVbXhs7vL+49bHfH2pfVcYTl5GDHZw7pYJn85bWdXCRKD0vXqv/KEc+x74LPeAl31gGy/GRXu/3vIker+Kgmz4Hf2nxzDNvJX3RGCuQLi2PVfJe+ncQRd5hhHZHDWe2SiaZKnt2n2AGc8+KJQbCIuuw9Lfoa2uQQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786689948; c=relaxed/simple; bh=zduZt5Yh8aK/cbqDe9szF+IP3dE7uqQwAz10EKTvkpY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CIv5Q+o8d06ougnEFO2a0+SrIibMWfNELGP2XLjta5rLyg9SJjIcwkpXrj23/O5AMlO6mxc9aGDqrrAsjlREZ+f6jvesgpH6YEL5zbXrmj7FnWYL6w50RnJTHYaSBz4Peb0rJdzP3lrw7MvrPiUPt5PD1slppOoBKWrFAqHoKGw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 61FB168BFE; Fri, 14 Aug 2026 08:45:37 +0200 (CEST) Date: Fri, 14 Aug 2026 08:45:37 +0200 From: Christoph Hellwig To: Yu Kuai Cc: Jens Axboe , Tejun Heo , Josef Bacik , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Yu Kuai , Christoph Hellwig , Tao Cui , Jan Kara , Ming Lei , Jonathan Corbet , Shuah Khan , Coly Li , Kent Overstreet , Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski , Song Liu , Li Nan , Xiao Ni , Pankaj Gupta , Dan Williams , Vishal Verma , Dave Jiang , Alison Schofield , Ira Weiny , Andreas Gruenbacher , Matthew Wilcox , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, dm-devel@lists.linux.dev, linux-raid@vger.kernel.org, nvdimm@lists.linux.dev, virtualization@lists.linux.dev, gfs2@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH v2 0/4] blk-cgroup: store blkcg in bio before blkcg_mutex conversion Message-ID: <20260814064537.GA9355@lst.de> References: <20260811064744.1139446-1-yukuai@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260811064744.1139446-1-yukuai@kernel.org> User-Agent: Mutt/1.5.17 (2007-11-01) What tree does this apply to? I get failures both for Jens' for-7.3/block and for-next trees in bfq-cgroups.c and bio.c On Tue, Aug 11, 2026 at 02:47:40PM +0800, Yu Kuai wrote: > From: Yu Kuai > > This RFC remains a preparatory series for the blkcg_mutex conversion > proposed in the related blkcg_mutex RFC v2 series [1]. That conversion > moves queue-local blkg topology synchronization from q->queue_lock to > q->blkcg_mutex, which is awkward while bios directly store queue-local > blkg references. > > v1 made the stored bio association queue-independent by replacing bi_blkg > with bi_blkcg, but a bio-owned blkg reference still had to be recovered by > looking up the bio's blkcg and current request_queue. Tao Cui reported that > cgroup removal deletes a dying blkg from the per-blkcg radix tree before a > throttled bio drops its reference. A later lookup for that pinned blkg then > fails, triggers the warning in bio_pinned_blkg(), and leaks the reference. > > v2 makes request_queue the authoritative lookup owner before converting the > bio association. A queue-owned rhashtable, keyed by the blkcg CSS ID, keeps > dying blkgs discoverable until their references drain while q->blkg_list > remains available for ordered walks. The bio conversion then stores and > pins the blkcg CSS, lazily creates a blkg only for users which need one, and > uses lookup-only access for completion and accounting paths which already > own a blkg reference. Async bio punt state is finally moved from blkg to > blkcg so punting alone does not instantiate a queue-local blkg. > > Changes since v1: > > - Add patch 1 to wait for every old blkg to leave q->blkg_list before a > shared request_queue is rebound, instead of treating root_blkg == NULL > as completion of asynchronous blkg teardown. > - Add patch 2 to replace the per-blkcg radix tree and lookup hint with a > request_queue rhashtable keyed by blkcg->css.id, as suggested by > Christoph Hellwig. Keep dying pinned blkgs in the hash until > blkg_release() so bio-owned references remain discoverable. > - Fold the v1 helper-only patch into patch 3, as suggested by Jan Kara and > Christoph Hellwig, and make bio_blkcg() naturally return NULL for an > unassociated bio. > - Rework patch 3 so blkg_lookup_create() acquires the bio-owned reference, > falls back to a live parent when creation or tryget fails, and updates > bi_blkcg when the returned blkg belongs to an ancestor. > - Make bio_blkg_lookup() lookup-only: it returns NULL unless BIO_BLKG_REF > is already set. Use bio_blkg() in the BFQ and IOCOST merge paths which > may need to create a blkg, while keeping blk_cgroup_bio_start() and > completion paths lookup-only. > - Move CSS online-reference handling into > bio_associate_blkcg_from_css(), including fallback to the root blkcg, so > bio_associate_blkcg() does not take a redundant reference. > - Keep the v1 async bio punt conversion as patch 4 and document that > async_bio_lock protects async_bios. > > Previous versions: > v1: https://lore.kernel.org/r/20260804065313.2092022-1-yukuai@kernel.org > > Related series: > [1] RFC v2 blk-cgroup: protect blkgs with blkcg_mutex > https://lore.kernel.org/r/20260724123037.3004560-1-yukuai@kernel.org > > Yu Kuai (4): > blk-cgroup: wait for old blkgs to leave queue before disk rebind > blk-cgroup: use a request_queue rhashtable for blkg lookup > blk-cgroup: store blkcg in bio instead of blkg > blk-cgroup: move async bio punt state to blkcg > > Documentation/admin-guide/cgroup-v2.rst | 2 +- > block/bfq-cgroup.c | 16 +- > block/bfq-iosched.c | 19 +- > block/bio.c | 22 +- > block/blk-cgroup-fc-appid.c | 10 +- > block/blk-cgroup.c | 348 ++++++++++++++---------- > block/blk-cgroup.h | 82 ++++-- > block/blk-core.c | 9 +- > block/blk-crypto-fallback.c | 2 +- > block/blk-iocost.c | 12 +- > block/blk-iolatency.c | 11 +- > block/blk-ioprio.c | 2 +- > block/blk-throttle.c | 2 +- > block/blk-throttle.h | 2 +- > drivers/md/bcache/request.c | 2 +- > drivers/md/dm.c | 2 +- > drivers/md/md.c | 2 +- > drivers/nvdimm/nd_virtio.c | 2 +- > fs/gfs2/lops.c | 3 +- > include/linux/bio.h | 26 +- > include/linux/blk_types.h | 9 +- > include/linux/blkdev.h | 2 + > include/linux/writeback.h | 2 +- > mm/page_io.c | 13 +- > 24 files changed, 357 insertions(+), 245 deletions(-) > > > base-commit: f2690679ecf3a3151688ebef766dd2512ff95854 > -- > 2.51.0 ---end quoted text---