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b=dZdUIubP7WawPPBoUISGeGIF5ET69n9vHrkUVvspPnrH7fxHweJj2pqEOElVx2vIL 0gFC5UbRFw2yyrUHY8PuEWsj3Mk6WHImCplwTlI60/XUI76P7v6YKqCFuBRQ3z6vC8 D4IfiDdtb9OpF9KJwyaUUmE0WCWrChqkCcnscAtjBVSlbLeT1gn8kIAGDPn7QXBRDy uyVZJ/cSvCjKvvkrk1SWqjkP71K7D2BHoKJ257aiaDDnQ+ozchaBZMGL59Cyc8YNCA cgNPGGgrw2vZkS3Mn+lrb1xgQs6YmdMPOv5u8KaDeiJ+0j1eeksXZuaT4qd7J9F0+p 3erBVRFc7D2AQ== From: Yu Kuai To: Jens Axboe , Josef Bacik , Tejun Heo , Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Jonathan Corbet , Shuah Khan , Randy Dunlap , Coly Li , Kent Overstreet , Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski , Song Liu , Li Nan , Xiao Ni , Andreas Gruenbacher , Matthew Wilcox , Jan Kara , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt Cc: Yu Kuai , Christoph Hellwig , Nilay Shroff , Tao Cui , linux-block@vger.kernel.org, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org, dm-devel@lists.linux.dev, linux-raid@vger.kernel.org, gfs2@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev Subject: [PATCH v3 0/3] blk-cgroup: store blkcg in bio before blkcg_mutex conversion Date: Fri, 18 Sep 2026 12:17:41 +0800 Message-ID: <20260918041744.1526924-1-yukuai@kernel.org> X-Mailer: git-send-email 2.51.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A0622180004 X-Stat-Signature: 3c1fqnzfxwfa7qjfmg645ewn8dj65n8q X-Rspam-User: X-HE-Tag: 1789705077-756559 X-HE-Meta: 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 5me7HnkH +1g4aI2njoaXWcdLaa8nDALzhQ6fWDVJYmL6N0dCNfFBI7FUQP+1dUylNxDcPS4yLjj/9kPXrB2dY68FKe/A165RNDUMCzFADvOjpN9M8DWMwGqkUqHJSokxpJ/k0lIwkQZvPxX22xEP46iRgPWTbhV3qYRMHK9a4DsRlDnB/axUjiSGDIAj8iBf6ThLSHDjlcWHVrJaLOePXiLcmfv2zZkgJCIMi54gjUCVEG+VXOFqtKXa4d55SRTWYHg1R3KON8u5a4r3c5VIafskCPwHiPHvOLd9x/0UB/8r9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Yu Kuai This is v3 of the preparatory series for the blkcg_mutex conversion proposed in the related 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. Storing a blkg also ties a bio to one request_queue. A remapped bio must drop that reference and recreate the association for the new queue even when no blkcg policy needs it. Dying blkgs add another complication: they disappear from the per-blkcg lookup tree before all pinned bio references drain. Patch 1 makes request_queue the authoritative lookup owner. 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. Patch 2 stores and pins the queue-independent blkcg CSS in each bio. Queue-local blkgs are created lazily by policy users, then pinned until the bio changes devices or releases its cgroup state. Completion and accounting paths which do not create a blkg remain lookup-only. Patch 3 moves async bio punt state from blkg to blkcg, so punting alone does not instantiate a queue-local blkg. Changes since v2: - Rebase onto the latest for-7.4/block branch. - In patch 2, clarify why dm_bio_record() excludes BIO_BLKG_REF and add Nilay Shroff's Reviewed-by. - In patch 3, replace scoped spinlock guards with explicit spin_lock()/spin_unlock(), drop the redundant teardown check, and rely on zero-initialization for async_bios before publication, as suggested by Nilay Shroff and Christoph Hellwig. Changes since v1: - Rebase onto the latest block-7.3 branch. - In patch 2, require every blkg rhashtable lookup to run inside an explicit RCU read-side critical section. Annotate blkg_lookup_any(), blkg_lookup(), and recursive wrappers with __must_hold_shared(RCU) so Clang thread-safety analysis verifies the contract. - In patch 2, exclude BIO_BLKG_REF from the flags saved by dm_bio_record(), since restoring an ownership bit cannot recreate the associated blkg reference. - In patch 3, use scoped spinlock guards for async_bios and annotate the list with __guarded_by(). - Add Nilay Shroff's Reviewed-by to patch 1. Changes since RFC v3: - Drop the RFC prefix. - Add Christoph Hellwig's Reviewed-by to patch 1. - Add Tao Cui's Reviewed-by to patch 2. - In patch 2, relax blkg_lookup_any()/blkg_lookup() to also allow q->queue_lock as an alternative to the RCU read lock. Changes since RFC v2: - Drop the old patch 1 and send it separately as a bugfix for 7.3 and -stable, as suggested by Christoph Hellwig. - Rebase onto the latest for-7.3/block branch. - In the new patch 1, note that the remaining q->blkg_list walkers are cgroupfs/sysfs slow paths and can move to rhashtable iteration after the queue_lock-to-blkcg_mutex conversion. - In the new patch 1, explain the list_empty case in blkg_release(), and add an RCU lockdep assertion plus documentation that blkg_lookup_any() does not acquire a reference. Changes since RFC 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: - v2: https://lore.kernel.org/r/cover.1789237876.git.yukuai@fygo.io - v1: https://lore.kernel.org/r/20260823133045.970199-1-yukuai@kernel.org - RFC v3: https://lore.kernel.org/r/20260818070641.756747-1-yukuai@kernel.org - RFC v2: https://lore.kernel.org/r/20260811064744.1139446-1-yukuai@kernel.org - RFC 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 (3): 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 | 18 +- block/bfq-iosched.c | 19 +- block/bio.c | 22 +- block/blk-cgroup-fc-appid.c | 10 +- block/blk-cgroup-rwstat.h | 2 +- block/blk-cgroup.c | 346 ++++++++++++++---------- block/blk-cgroup.h | 93 +++++-- 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 | 3 +- block/blk-throttle.h | 2 +- drivers/md/bcache/request.c | 2 +- drivers/md/dm-bio-record.h | 5 +- drivers/md/dm.c | 2 +- drivers/md/md.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 | 12 +- 25 files changed, 381 insertions(+), 237 deletions(-) base-commit: af78ca007be5f63dc34b8180c8063c1113697192 -- 2.51.0