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Wed, 04 Dec 2024 05:02:36 -0500 X-MC-Unique: Wxw75sU_M6qlKAMlK1FbfA-1 X-Mimecast-MFC-AGG-ID: Wxw75sU_M6qlKAMlK1FbfA Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A9E5B1954ADC; Wed, 4 Dec 2024 10:02:34 +0000 (UTC) Received: from fedora (unknown [10.72.112.144]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 359A019560A2; Wed, 4 Dec 2024 10:02:28 +0000 (UTC) Date: Wed, 4 Dec 2024 18:02:23 +0800 From: Ming Lei To: Qiang Ma Cc: James.Bottomley@hansenpartnership.com, martin.petersen@oracle.com, axboe@kernel.dk, dwagner@suse.de, hare@suse.de, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] scsi: Don't wait for completion of in-flight requests Message-ID: References: <20241126115008.31272-1-maqianga@uniontech.com> <2100C70C0D4CA64E+20241127220437.65ae99dd@john-PC> Precedence: bulk X-Mailing-List: linux-scsi@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: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On Wed, Dec 04, 2024 at 04:45:57PM +0800, Qiang Ma wrote: > On Tue, 3 Dec 2024 22:36:47 +0800 > Ming Lei wrote: > > > On Tue, Dec 03, 2024 at 09:21:04PM +0800, Qiang Ma wrote: > > > On Wed, 27 Nov 2024 23:20:28 +0800 > > > Ming Lei wrote: > > > > > > > On Wed, Nov 27, 2024 at 10:04:37PM +0800, Qiang Ma wrote: > > > > > On Tue, 26 Nov 2024 22:15:02 +0800 > > > > > Ming Lei wrote: > > > > > > > > > > > On Tue, Nov 26, 2024 at 07:50:08PM +0800, Qiang Ma wrote: > > > > > > > Problem: > > > > > > > When the system disk uses the scsi disk bus, The main > > > > > > > qemu command line includes: > > > > > > > ... > > > > > > > -device virtio-scsi-pci,id=scsi0 \ > > > > > > > -device scsi-hd,scsi-id=1,drive=drive-virtio-disk > > > > > > > -drive > > > > > > > id=drive-virtio-disk,if=none,file=/home/kvm/test.qcow2 ... > > > > > > > > > > > > > > The dmesg log is as follows:: > > > > > > > > > > > > > > [ 50.304591][ T4382] sd 0:0:0:0: [sda] Synchronizing SCSI > > > > > > > cache [ 50.377002][ T4382] kexec_core: Starting new > > > > > > > kernel > > > > > > > > Why is one new kernel started? what event triggers kernel_kexec()? > > > > > > > > machine_shutdown() follows, probably the scsi controller is dead. > > > > > > > > > > Yes, triggered by kexec, manually execute the following command: > > > kexec -l /boot/vmlinuz-6.6.0+ --reuse-cmdline > > > --initrd=/boot/initramfs-6.6.0+.img kexec -e > > > > > > > > > > [ 50.669775][ T194] psci: CPU1 killed (polled 0 ms) > > > > > > > [ 50.849665][ T194] psci: CPU2 killed (polled 0 ms) > > > > > > > [ 51.109625][ T194] psci: CPU3 killed (polled 0 ms) > > > > > > > [ 51.319594][ T194] psci: CPU4 killed (polled 0 ms) > > > > > > > [ 51.489667][ T194] psci: CPU5 killed (polled 0 ms) > > > > > > > [ 51.709582][ T194] psci: CPU6 killed (polled 0 ms) > > > > > > > [ 51.949508][ T10] psci: CPU7 killed (polled 0 ms) > > > > > > > [ 52.139499][ T10] psci: CPU8 killed (polled 0 ms) > > > > > > > [ 52.289426][ T10] psci: CPU9 killed (polled 0 ms) > > > > > > > [ 52.439552][ T10] psci: CPU10 killed (polled 0 ms) > > > > > > > [ 52.579525][ T10] psci: CPU11 killed (polled 0 ms) > > > > > > > [ 52.709501][ T10] psci: CPU12 killed (polled 0 ms) > > > > > > > [ 52.819509][ T194] psci: CPU13 killed (polled 0 ms) > > > > > > > [ 52.919509][ T194] psci: CPU14 killed (polled 0 ms) > > > > > > > [ 243.214009][ T115] INFO: task kworker/0:1:10 blocked for > > > > > > > more than 122 seconds. [ 243.214810][ T115] Not > > > > > > > tainted 6.6.0+ #1 [ 243.215517][ T115] "echo 0 > > > > > > > > /proc/sys/kernel/hung_task_timeout_secs" disables this > > > > > > > > message. [ 243.216390][ T115] task:kworker/0:1 > > > > > > > > state:D stack:0 pid:10 ppid:2 flags:0x00000008 > > > > > > > [ 243.217299][ T115] Workqueue: events vmstat_shepherd > > > > > > > [ 243.217816][ T115] Call trace: > > > > > > > [ 243.218133][ T115] __switch_to+0x130/0x1e8 > > > > > > > [ 243.218568][ T115] __schedule+0x660/0xcf8 > > > > > > > [ 243.219013][ T115] schedule+0x58/0xf0 > > > > > > > [ 243.219402][ T115] percpu_rwsem_wait+0xb0/0x1d0 > > > > > > > [ 243.219880][ T115] __percpu_down_read+0x40/0xe0 > > > > > > > [ 243.220353][ T115] cpus_read_lock+0x5c/0x70 > > > > > > > [ 243.220795][ T115] vmstat_shepherd+0x40/0x140 > > > > > > > [ 243.221250][ T115] process_one_work+0x170/0x3c0 > > > > > > > [ 243.221726][ T115] worker_thread+0x234/0x3b8 > > > > > > > [ 243.222176][ T115] kthread+0xf0/0x108 > > > > > > > [ 243.222564][ T115] ret_from_fork+0x10/0x20 > > > > > > > ... > > > > > > > [ 243.254080][ T115] INFO: task kworker/0:2:194 blocked > > > > > > > for more than 122 seconds. [ 243.254834][ T115] Not > > > > > > > tainted 6.6.0+ #1 [ 243.255529][ T115] "echo 0 > > > > > > > > /proc/sys/kernel/hung_task_timeout_secs" disables this > > > > > > > > message. [ 243.256378][ T115] task:kworker/0:2 > > > > > > > > state:D stack:0 pid:194 ppid:2 flags:0x00000008 > > > > > > > [ 243.257284][ T115] Workqueue: events work_for_cpu_fn > > > > > > > [ 243.257793][ T115] Call trace: > > > > > > > [ 243.258111][ T115] __switch_to+0x130/0x1e8 > > > > > > > [ 243.258541][ T115] __schedule+0x660/0xcf8 > > > > > > > [ 243.258971][ T115] schedule+0x58/0xf0 > > > > > > > [ 243.259360][ T115] schedule_timeout+0x280/0x2f0 > > > > > > > [ 243.259832][ T115] wait_for_common+0xcc/0x2d8 > > > > > > > [ 243.260287][ T115] wait_for_completion+0x20/0x38 > > > > > > > [ 243.260767][ T115] cpuhp_kick_ap+0xe8/0x278 > > > > > > > [ 243.261207][ T115] cpuhp_kick_ap_work+0x5c/0x188 > > > > > > > [ 243.261688][ T115] _cpu_down+0x120/0x378 > > > > > > > [ 243.262103][ T115] __cpu_down_maps_locked+0x20/0x38 > > > > > > > [ 243.262609][ T115] work_for_cpu_fn+0x24/0x40 > > > > > > > [ 243.263059][ T115] process_one_work+0x170/0x3c0 > > > > > > > [ 243.263533][ T115] worker_thread+0x234/0x3b8 > > > > > > > [ 243.263981][ T115] kthread+0xf0/0x108 > > > > > > > [ 243.264405][ T115] ret_from_fork+0x10/0x20 > > > > > > > [ 243.264846][ T115] INFO: task kworker/15:2:639 blocked > > > > > > > for more than 122 seconds. [ 243.265602][ T115] Not > > > > > > > tainted 6.6.0+ #1 [ 243.266296][ T115] "echo 0 > > > > > > > > /proc/sys/kernel/hung_task_timeout_secs" disables this > > > > > > > > message. [ 243.267143][ T115] task:kworker/15:2 > > > > > > > > state:D stack:0 pid:639 ppid:2 flags:0x00000008 > > > > > > > [ 243.268044][ T115] Workqueue: events_freezable_power_ > > > > > > > disk_events_workfn [ 243.268727][ T115] Call trace: > > > > > > > [ 243.269051][ T115] __switch_to+0x130/0x1e8 > > > > > > > [ 243.269481][ T115] __schedule+0x660/0xcf8 > > > > > > > [ 243.269903][ T115] schedule+0x58/0xf0 > > > > > > > [ 243.270293][ T115] schedule_timeout+0x280/0x2f0 > > > > > > > [ 243.270763][ T115] io_schedule_timeout+0x50/0x70 > > > > > > > [ 243.271245][ T115] > > > > > > > wait_for_common_io.constprop.0+0xb0/0x298 > > > > > > > [ 243.271830][ T115] wait_for_completion_io+0x1c/0x30 > > > > > > > [ 243.272335][ T115] blk_execute_rq+0x1d8/0x278 > > > > > > > [ 243.272793][ T115] scsi_execute_cmd+0x114/0x238 > > > > > > > [ 243.273267][ T115] sr_check_events+0xc8/0x310 [sr_mod] > > > > > > > [ 243.273808][ T115] cdrom_check_events+0x2c/0x50 [cdrom] > > > > > > > [ 243.274408][ T115] sr_block_check_events+0x34/0x48 > > > > > > > [sr_mod] [ 243.274994][ T115] > > > > > > > disk_check_events+0x44/0x1b0 [ 243.275468][ T115] > > > > > > > disk_events_workfn+0x20/0x38 [ 243.275939][ T115] > > > > > > > process_one_work+0x170/0x3c0 [ 243.276410][ T115] > > > > > > > worker_thread+0x234/0x3b8 [ 243.276855][ T115] > > > > > > > kthread+0xf0/0x108 [ 243.277241][ T115] > > > > > > > ret_from_fork+0x10/0x20 > > > > > > > > > > > > Question is why this scsi command can't be completed? > > > > > > > > > > > > When blk_mq_hctx_notify_offline() is called, the CPU isn't > > > > > > shutdown yet, and it still can handle interrupt of this SCSI > > > > > > command. > > > > > > > > > > > > > > > > > > Thanks, > > > > > > Ming > > > > > > > > > > > > > > > > > Sorry, at the moment I don't know why it can't be finished, > > > > > just provides a solution like loop and dm-rq. > > > > > > > > > > Currently see the call stack: > > > > > => blk_mq_run_hw_queue > > > > > =>__blk_mq_sched_restart > > > > > => blk_mq_run_hw_queue > > > > > => __blk_mq_sched_restart > > > > > => __blk_mq_free_request > > > > > => blk_mq_free_request > > > > > => blk_mq_end_request > > > > > => blk_flush_complete_seq > > > > > => flush_end_io > > > > > => __blk_mq_end_request > > > > > => scsi_end_request > > > > > => scsi_io_completion > > > > > => scsi_finish_command > > > > > => scsi_complete > > > > > => blk_mq_complete_request > > > > > => scsi_done_internal > > > > > => scsi_done > > > > > => virtscsi_complete_cmd > > > > > => virtscsi_req_done > > > > > => vring_interrupt > > > > > > > > > > In finction blk_mq_run_hw_queue(): > > > > > __blk_mq_run_dispatch_ops(hctx->queue, false, > > > > > need_run = !blk_queue_quiesced(hctx->queue) && > > > > > blk_mq_hctx_has_pending(hctx)); > > > > > > > > > > if (!need_run) > > > > > return; > > > > > > > > > > Come here and return directly. > > > > > > > > Does blk_queue_quiesced() return true? > > > > > > > > > > blk_queue_quiesced() return false > > > > > > Sorry, the calltrace above is not the one that is stuck this time. > > > The hang is caused by the wait_for_completion_io(), in > > > blk_execute_rq(): > > > > > > blk_status_t blk_execute_rq(struct request *rq, bool at_head) > > > { > > > ... > > > rq->end_io_data = &wait; > > > rq->end_io = blk_end_sync_rq; > > > ... > > > blk_account_io_start(rq); > > > blk_mq_insert_request(rq, at_head ? BLK_MQ_INSERT_AT_HEAD : > > > 0); blk_mq_run_hw_queue(hctx, false); > > > > > > if (blk_rq_is_poll(rq)) { > > > blk_rq_poll_completion(rq, &wait.done); > > > } else { > > > ... > > > wait_for_completion_io(&wait.done); > > > } > > > } > > > > > > In this case, end_io is blk_end_sync_rq, which is not executed. > > > > > > The process for sending scsi commands is as follows: > > > > > > kworker/7:1-134 [007] ..... 32.772727: vp_notify > > > <-virtqueue_notify kworker/7:1-134 [007] ..... > > > 32.772729: => vp_notify > > > => virtqueue_notify > > > => virtscsi_add_cmd > > > => virtscsi_queuecommand > > > => scsi_dispatch_cmd > > > => scsi_queue_rq > > > => blk_mq_dispatch_rq_list > > > => __blk_mq_sched_dispatch_requests > > > => blk_mq_sched_dispatch_requests > > > => blk_mq_run_hw_queue > > > => blk_execute_rq > > > => scsi_execute_cmd > > > => sr_check_events > > > => cdrom_check_events > > > => sr_block_check_events > > > => disk_check_events > > > => disk_events_workfn > > > => process_one_work > > > => worker_thread > > > => kthread > > > => ret_from_fork > > > > > > In qemu: > > > static void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq) > > > { > > > ... > > > do { > > > if (suppress_notifications) { > > > virtio_queue_set_notification(vq, 0); > > > } > > > ... > > > } while (ret != -EINVAL && !virtio_queue_empty(vq)); > > > ... > > > QTAILQ_FOREACH_SAFE(req, &reqs, next, next) { > > > virtio_scsi_handle_cmd_req_submit(s, req); > > > } > > > } > > > > > > virtio_queue_empty() always return true. > > > > > > As a result, the virtio_scsi_handle_cmd_req_submit() was not > > > executed, and the io command was never submitted. > > > > > > The reason is that virtio_device_disabled returns true in > > > virtio_queue_split_empty, the code is as follows: > > > > > > int virtio_queue_empty(VirtQueue *vq) > > > { > > > if (virtio_vdev_has_feature(vq->vdev, > > > VIRTIO_F_RING_PACKED)) { return virtio_queue_packed_empty(vq); > > > } else { > > > return virtio_queue_split_empty(vq); > > > } > > > } > > > > > > static int virtio_queue_split_empty(VirtQueue *vq) > > > { > > > bool empty; > > > > > > if (virtio_device_disabled(vq->vdev)) { > > > return 1; > > > ... > > > } > > > > > > This function was introduced in the following patch: > > > > > > commit 9d7bd0826f2d19f88631ad7078662668148f7b5f > > > Author: Michael Roth > > > Date: Tue Nov 19 18:50:03 2019 -0600 > > > > > > virtio-pci: disable vring processing when bus-mastering is > > > disabled > > > > OK, then it is obviously one qemu issue, and it can explain why IO > > isn't completed in this case. > > > > > > However, in fact, the current pci-master state is disabled, it is > shutdown by executing the syscore_shutdown() in kernel_kexec(), and the > call stack is as follows: > kernel_kexec > => syscore_shutdown > => ops->shutdown > => pci_device_shutdown > => pci_clear_master > => __pci_set_master > > Therefore, qemu determines the pci-master status and disable > virtio-pci when tthe state of the pci-master is disabled. But either virtio-scsi driver or qemu knows clearly that there is one in-flight request not completed, and is just ignored silently. Anyway, it is not one issue in block layer or scsi-core code. Thanks, Ming