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Thu, 04 Dec 2025 11:15:58 -0800 (PST) Date: Thu, 4 Dec 2025 11:15:55 -0800 From: Mohamed Khalfella To: Bart Van Assche Cc: Chaitanya Kulkarni , Christoph Hellwig , Jens Axboe , Keith Busch , Sagi Grimberg , Casey Chen , Yuanyuan Zhong , Hannes Reinecke , Ming Lei , Waiman Long , Hillf Danton , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] block: Use RCU in blk_mq_[un]quiesce_tagset() instead of set->tag_list_lock Message-ID: <20251204191555.GB337106-mkhalfella@purestorage.com> References: <20251204181212.1484066-1-mkhalfella@purestorage.com> <20251204181212.1484066-2-mkhalfella@purestorage.com> <5450d3fa-3f00-40ae-ac95-1f08886de3b6@acm.org> <20251204184243.GZ337106-mkhalfella@purestorage.com> <71e9950f-ace7-4570-a604-ceca347eea20@acm.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: <71e9950f-ace7-4570-a604-ceca347eea20@acm.org> On Thu 2025-12-04 09:06:47 -1000, Bart Van Assche wrote: > On 12/4/25 8:42 AM, Mohamed Khalfella wrote: > > Is blk_mq_del_queue_tag_set() performance sensitive such that it can not > > take synchronize_rcu()? It is not in IO codepath, right? > > Introducing a new synchronize_rcu() call almost always slows down some > workload so it should be avoided if possible. > > > I can not think of an easy way to do that. Suggestions are welcomed. > > I can't find the implementation of nvme_dev_disable_locked(). What > kernel tree does your patch apply to? > > $ git grep -w nvme_dev_disable_locked axboe-block/for-next | wc -l > 0 The stacktraces are from old 6.6.9 kernel. However, the issue is still applicable to recent kernels. This is an example from 6.13 kernel. Oct 1 15:19:30 hostname kernel: INFO: task kworker/151:1H:2442 blocked for more than 122 seconds. Oct 1 15:19:30 hostname kernel: Tainted: G E 6.13.2-ge5f37b497f62 #1 Oct 1 15:19:30 hostname kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Oct 1 15:19:30 hostname kernel: task:kworker/151:1H state:D stack:0 pid:2442 tgid:2442 ppid:2 flags:0x00004000 Oct 1 15:19:30 hostname kernel: Workqueue: kblockd blk_mq_timeout_work Oct 1 15:19:30 hostname kernel: Call Trace: Oct 1 15:19:30 hostname kernel: Oct 1 15:19:30 hostname kernel: __schedule+0x47c/0xbb0 Oct 1 15:19:30 hostname kernel: ? timerqueue_add+0x66/0xb0 Oct 1 15:19:30 hostname kernel: schedule+0x1c/0xa0 Oct 1 15:19:30 hostname kernel: schedule_preempt_disabled+0xa/0x10 Oct 1 15:19:30 hostname kernel: __mutex_lock.constprop.0+0x271/0x600 Oct 1 15:19:30 hostname kernel: blk_mq_quiesce_tagset+0x25/0xc0 Oct 1 15:19:30 hostname kernel: nvme_dev_disable+0x9c/0x250 Oct 1 15:19:30 hostname kernel: nvme_timeout+0x1fc/0x520 Oct 1 15:19:30 hostname kernel: blk_mq_handle_expired+0x5c/0x90 Oct 1 15:19:30 hostname kernel: bt_iter+0x7e/0x90 Oct 1 15:19:30 hostname kernel: blk_mq_queue_tag_busy_iter+0x27e/0x550 Oct 1 15:19:30 hostname kernel: ? __blk_mq_complete_request_remote+0x10/0x10 Oct 1 15:19:30 hostname kernel: ? __blk_mq_complete_request_remote+0x10/0x10 Oct 1 15:19:30 hostname kernel: ? __call_rcu_common.constprop.0+0x1c0/0x210 Oct 1 15:19:30 hostname kernel: blk_mq_timeout_work+0x12d/0x170 Oct 1 15:19:30 hostname kernel: process_one_work+0x12e/0x2d0 Oct 1 15:19:30 hostname kernel: worker_thread+0x288/0x3a0 Oct 1 15:19:30 hostname kernel: ? rescuer_thread+0x480/0x480 Oct 1 15:19:30 hostname kernel: kthread+0xb8/0xe0 Oct 1 15:19:30 hostname kernel: ? kthread_park+0x80/0x80 Oct 1 15:19:30 hostname kernel: ret_from_fork+0x2d/0x50 Oct 1 15:19:30 hostname kernel: ? kthread_park+0x80/0x80 Oct 1 15:19:30 hostname kernel: ret_from_fork_asm+0x11/0x20 Oct 1 15:19:30 hostname kernel: Oct 1 15:19:30 hostname kernel: INFO: task python:37330 blocked for more than 122 seconds. Oct 1 15:19:30 hostname kernel: Tainted: G E 6.13.2-ge5f37b497f62 #1 Oct 1 15:19:30 hostname kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Oct 1 15:19:30 hostname kernel: task:python state:D stack:0 pid:37330 tgid:37330 ppid:37329 flags:0x00004002 Oct 1 15:19:30 hostname kernel: Call Trace: Oct 1 15:19:30 hostname kernel: Oct 1 15:19:30 hostname kernel: __schedule+0x47c/0xbb0 Oct 1 15:19:30 hostname kernel: ? xas_find+0x161/0x1a0 Oct 1 15:19:30 hostname kernel: schedule+0x1c/0xa0 Oct 1 15:19:30 hostname kernel: blk_mq_freeze_queue_wait+0x3d/0x70 Oct 1 15:19:30 hostname kernel: ? destroy_sched_domains_rcu+0x30/0x30 Oct 1 15:19:30 hostname kernel: blk_mq_update_tag_set_shared+0x44/0x80 Oct 1 15:19:30 hostname kernel: blk_mq_exit_queue+0x141/0x150 Oct 1 15:19:30 hostname kernel: del_gendisk+0x25a/0x2d0 Oct 1 15:19:30 hostname kernel: nvme_ns_remove+0xc9/0x170 Oct 1 15:19:30 hostname kernel: nvme_remove_namespaces+0xc7/0x100 Oct 1 15:19:30 hostname kernel: nvme_remove+0x62/0x150 Oct 1 15:19:30 hostname kernel: pci_device_remove+0x23/0x60 Oct 1 15:19:30 hostname kernel: device_release_driver_internal+0x159/0x200 Oct 1 15:19:30 hostname kernel: unbind_store+0x99/0xa0 Oct 1 15:19:30 hostname kernel: kernfs_fop_write_iter+0x112/0x1e0 Oct 1 15:19:30 hostname kernel: vfs_write+0x2b1/0x3d0 Oct 1 15:19:30 hostname kernel: ksys_write+0x4e/0xb0 Oct 1 15:19:30 hostname kernel: do_syscall_64+0x5b/0x160 Oct 1 15:19:30 hostname kernel: entry_SYSCALL_64_after_hwframe+0x4b/0x53 Oct 1 15:19:30 hostname kernel: RIP: 0033:0x7f12cf2fe02f Oct 1 15:19:30 hostname kernel: RSP: 002b:00007f12311f78e0 EFLAGS: 00000293 ORIG_RAX: 0000000000000001 Oct 1 15:19:30 hostname kernel: RAX: ffffffffffffffda RBX: 00007f12311ff5c8 RCX: 00007f12cf2fe02f Oct 1 15:19:30 hostname kernel: RDX: 000000000000000c RSI: 00007f12081c19a0 RDI: 000000000000003b Oct 1 15:19:30 hostname kernel: RBP: 000000000000000c R08: 0000000000000000 R09: 0000000000000002 Oct 1 15:19:30 hostname kernel: R10: 0000000000000002 R11: 0000000000000293 R12: 00007f12cae00700 Oct 1 15:19:30 hostname kernel: R13: 00007f12081c19a0 R14: 000000000000003b R15: 00007f1220219990 Oct 1 15:19:30 hostname kernel: > > Thanks, > > Bart.