[PATCH] scsi: Don't wait for completion of in-flight requests

[Qiang Ma <maqianga@uniontech.com>]

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@uniontech.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;
 	tag_set->flags |=
 		BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
 	if (shost->queuecommand_may_block)
-- 
2.20.1