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Message-ID: <3472C3D5E7A545A1+20241127215330.493f9690@john-PC>
Date: Wed, 27 Nov 2024 21:53:30 +0800
From: Qiang Ma <maqianga@...ontech.com>
To: John Garry <john.g.garry@...cle.com>
Cc: James.Bottomley@...senPartnership.com, martin.petersen@...cle.com,
axboe@...nel.dk, dwagner@...e.de, ming.lei@...hat.com, hare@...e.de,
linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: Don't wait for completion of in-flight requests
On Tue, 26 Nov 2024 12:21:24 +0000
John Garry <john.g.garry@...cle.com> wrote:
> On 26/11/2024 11:50, 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
> > [ 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
> >
> > ftrace finds that it enters an endless loop, code as follows:
> >
> > if (percpu_ref_tryget(&hctx->queue->q_usage_counter)) {
> > while (blk_mq_hctx_has_requests(hctx))
> > msleep(5);
> > percpu_ref_put(&hctx->queue->q_usage_counter);
> > }
> >
> > Solution:
> > Refer to the loop and dm-rq in patch commit bf0beec0607d
> > ("blk-mq: drain I/O when all CPUs in a hctx are offline"),
> > add a BLK_MQ_F_STACKING and set it for scsi, so we don't need
> > to wait for completion of in-flight requests to avoid a potential
> > hung task.
> >
> > Fixes: bf0beec0607d ("blk-mq: drain I/O when all CPUs in a hctx are
> > offline")
> >
> > Signed-off-by: Qiang Ma <maqianga@...ontech.com>
> > ---
> > drivers/scsi/scsi_lib.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> > index adee6f60c966..0a2d5d9327fc 100644
> > --- a/drivers/scsi/scsi_lib.c
> > +++ b/drivers/scsi/scsi_lib.c
> > @@ -2065,7 +2065,7 @@ int scsi_mq_setup_tags(struct Scsi_Host
> > *shost) tag_set->queue_depth = shost->can_queue;
> > tag_set->cmd_size = cmd_size;
> > tag_set->numa_node = dev_to_node(shost->dma_dev);
> > - tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
> > + tag_set->flags = BLK_MQ_F_SHOULD_MERGE |
> > BLK_MQ_F_STACKING;
>
> This should not be set for all SCSI hosts. Some SCSI hosts rely on
> bf0beec0607d.
>
>
What are the side effects of setting this up for some scsi hosts?
> > tag_set->flags |=
> > BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
> > if (shost->queuecommand_may_block)
>
>
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