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Sun, 06 Sep 2026 10:57:14 +0000 (GMT) Received: from smtpav05.dal12v.mail.ibm.com (smtpav05.dal12v.mail.ibm.com [10.241.53.104]) by smtprelay01.wdc07v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 686AvDaR63242526 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sun, 6 Sep 2026 10:57:14 GMT Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AA76C58052; Sun, 6 Sep 2026 10:57:13 +0000 (GMT) Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CC6575805D; Sun, 6 Sep 2026 10:56:51 +0000 (GMT) Received: from [9.61.37.159] (unknown [9.61.37.159]) by smtpav05.dal12v.mail.ibm.com (Postfix) with ESMTP; Sun, 6 Sep 2026 10:56:51 +0000 (GMT) Message-ID: <49d724b8-57c6-48fc-8099-69cd1b072351@linux.ibm.com> Date: Sun, 6 Sep 2026 16:26:49 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] blk-cgroup: store blkcg in bio instead of blkg To: Yu Kuai , Jens Axboe , Tejun Heo , Josef Bacik , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= Cc: Yu Kuai , Christoph Hellwig , Tao Cui , Jan Kara , 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 References: <20260823133045.970199-1-yukuai@kernel.org> <20260823133045.970199-3-yukuai@kernel.org> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20260823133045.970199-3-yukuai@kernel.org> Content-Type: text/plain; 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The caller must already hold one, or > * have the blkg pinned by I/O. > */ > static inline struct blkcg_gq *blkg_lookup_any(struct blkcg *blkcg, > struct request_queue *q) > { > - RCU_LOCKDEP_WARN(!rcu_read_lock_held(), > - "blkg_lookup_any() requires an RCU read lock"); > + RCU_LOCKDEP_WARN(!rcu_read_lock_held() && > + !lockdep_is_held(&q->queue_lock), > + "blkg_lookup_any() requires an RCU read lock or queue_lock"); > > return rhashtable_lookup(&q->blkg_hash, &blkcg->css.id, > blkg_hash_params); > } The changes look good to me. However, rhashtable_lookup() is annotated with __must_hold_shared(RCU). Since we now officially support Clang context annotations in the block layer, compiling with the latest Clang/LLVM generates a number of context warnings, for example: block/blk-cgroup.h:277:9: warning: calling function 'rhashtable_lookup' requires holding __ctx_lock_RCU 'RCU' [-Wthread-safety-analysis] 277 | return rhashtable_lookup(&q->blkg_hash, &blkcg->css.id, | ^ The same warning is reported from several other block layer source files that include blk-cgroup.h. This indicates that rhashtable_lookup() requires the RCU read lock from Clang's context-analysis perspective. Looking at the call paths of blkg_lookup_any(), it appears that not all callers hold rcu_read_lock() when invoking it. I think we should fix those call paths to acquire rcu reader lock before calling blkg_lookup_any(), rather than weakening or bypassing the context annotation in blkg_lookup_any(). Thanks, --Nilay