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