Well, last_avail_idx equals to shadow_avail_idx and both of them are 1
at the qemu side. So, only one request is transferred.
I wonder why, probably something is badly cached, but new avail_idx
(which is supposed to become 2) is never shown up.

2018-02-20 15:49 GMT+03:00 Matwey V. Kornilov <email address hidden>:
> virtqueue_pop() returns NULL due to virtio_queue_empty_rcu() returns
> true all the time.
>
> 2018-02-20 14:47 GMT+03:00 Matwey V. Kornilov <email address hidden>:
>> Well, I've found that on qemu side VirtQueue for virtio_blk device
>> infinitely calls virtio_blk_handle_vq() where virtio_blk_get_request()
>> (virtqueue_pop() in essens) always returns NULL.
>>
>> 2018-02-18 15:26 GMT+03:00 Matwey V. Kornilov <email address hidden>:
>>> ** Attachment added: ".build.kernel.kvm"
>>>    https://bugs.launchpad.net/qemu/+bug/1750229/+attachment/5057653/+files/.build.kernel.kvm
>>>
>>> --
>>> You received this bug notification because you are subscribed to the bug
>>> report.
>>> https://bugs.launchpad.net/bugs/1750229
>>>
>>> Title:
>>>   virtio-blk-pci regression: softlock in guest kernel at module loading
>>>
>>> Status in QEMU:
>>>   New
>>>
>>> Bug description:
>>>   Hello,
>>>
>>>   I am running qemu from master git branch on x86_64 host with kernel is
>>>   4.4.114. I've found that commit
>>>
>>>       9a4c0e220d8a "hw/virtio-pci: fix virtio behaviour"
>>>
>>>   introduces an regression with the following command:
>>>
>>>       qemu-system-x86_64 -enable-kvm -nodefaults -no-reboot -nographic
>>>   -vga none -runas qemu -kernel .build.kernel.kvm -initrd
>>>   .build.initrd.kvm -append 'panic=1 softlockup_panic=1 no-kvmclock
>>>   nmi_watchdog=0 console=ttyS0 root=/dev/disk/by-id/virtio-0' -m 2048
>>>   -drive file=./root,format=raw,if=none,id=disk,serial=0,cache=unsafe
>>>   -device virtio-blk-pci,drive=disk -serial stdio -smp 2
>>>
>>>   Starting from this commit to master the following happens with a wide
>>>   variety of guest kernels (4.4 to 4.15):
>>>
>>>   [   62.428107] BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=-20 stuck for 59s!
>>>   [   62.437426] Showing busy workqueues and worker pools:
>>>   [   62.443117] workqueue events: flags=0x0
>>>   [   62.447512]   pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256
>>>   [   62.448161]     pending: check_corruption
>>>   [   62.458570] workqueue kblockd: flags=0x18
>>>   [   62.463082]   pwq 1: cpus=0 node=0 flags=0x0 nice=-20 active=3/256
>>>   [   62.463082]     in-flight: 4:blk_mq_run_work_fn
>>>   [   62.463082]     pending: blk_mq_run_work_fn, blk_mq_timeout_work
>>>   [   62.474831] pool 1: cpus=0 node=0 flags=0x0 nice=-20 hung=59s workers=2 idle: 214
>>>   [   62.492121] INFO: rcu_preempt detected stalls on CPUs/tasks:
>>>   [   62.492121]  Tasks blocked on level-0 rcu_node (CPUs 0-1): P4
>>>   [   62.492121]  (detected by 0, t=15002 jiffies, g=-130, c=-131, q=32)
>>>   [   62.492121] kworker/0:0H    R  running task        0     4      2 0x80000000
>>>   [   62.492121] Workqueue: kblockd blk_mq_run_work_fn
>>>   [   62.492121] Call Trace:
>>>   [   62.492121]  <IRQ>
>>>   [   62.492121]  sched_show_task+0xdf/0x100
>>>   [   62.492121]  rcu_print_detail_task_stall_rnp+0x48/0x69
>>>   [   62.492121]  rcu_check_callbacks+0x93d/0x9d0
>>>   [   62.492121]  ? tick_sched_do_timer+0x40/0x40
>>>   [   62.492121]  update_process_times+0x28/0x50
>>>   [   62.492121]  tick_sched_handle+0x22/0x70
>>>   [   62.492121]  tick_sched_timer+0x34/0x70
>>>   [   62.492121]  __hrtimer_run_queues+0xcc/0x250
>>>   [   62.492121]  hrtimer_interrupt+0xab/0x1f0
>>>   [   62.492121]  smp_apic_timer_interrupt+0x62/0x150
>>>   [   62.492121]  apic_timer_interrupt+0xa2/0xb0
>>>   [   62.492121]  </IRQ>
>>>   [   62.492121] RIP: 0010:iowrite16+0x1d/0x30
>>>   [   62.492121] RSP: 0018:ffffa477c034fcc8 EFLAGS: 00010292 ORIG_RAX: ffffffffffffff11
>>>   [   62.492121] RAX: ffffffffa24fbdb0 RBX: ffff92a1f8f82000 RCX: 0000000000000001
>>>   [   62.492121] RDX: ffffa477c0371000 RSI: ffffa477c0371000 RDI: 0000000000000000
>>>   [   62.492121] RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000001080020
>>>   [   62.492121] R10: ffffdc7cc1e4fc00 R11: 0000000000000000 R12: 0000000000000000
>>>   [   62.492121] R13: 0000000000000000 R14: ffff92a1f93f0000 R15: ffff92a1f8e1aa80
>>>   [   62.492121]  ? vp_synchronize_vectors+0x60/0x60
>>>   [   62.492121]  vp_notify+0x12/0x20
>>>   [   62.492121]  virtqueue_notify+0x18/0x30
>>>   [   62.492121]  virtio_queue_rq+0x2f5/0x300 [virtio_blk]
>>>   [   62.492121]  blk_mq_dispatch_rq_list+0x7e/0x4a0
>>>   [   62.492121]  blk_mq_do_dispatch_sched+0x4a/0xd0
>>>   [   62.492121]  blk_mq_sched_dispatch_requests+0x106/0x170
>>>   [   62.492121]  __blk_mq_run_hw_queue+0x80/0x90
>>>   [   62.492121]  process_one_work+0x1e3/0x420
>>>   [   62.492121]  worker_thread+0x2b/0x3d0
>>>   [   62.492121]  ? process_one_work+0x420/0x420
>>>   [   62.492121]  kthread+0x113/0x130
>>>   [   62.492121]  ? kthread_create_worker_on_cpu+0x50/0x50
>>>   [   62.492121]  ret_from_fork+0x3a/0x50
>>>   [   62.492121] kworker/0:0H    R  running task        0     4      2 0x80000000
>>>   [   62.492121] Workqueue: kblockd blk_mq_run_work_fn
>>>   [   62.492121] Call Trace:
>>>   [   62.492121]  <IRQ>
>>>   [   62.492121]  sched_show_task+0xdf/0x100
>>>   [   62.492121]  rcu_print_detail_task_stall_rnp+0x48/0x69
>>>   [   62.492121]  rcu_check_callbacks+0x972/0x9d0
>>>   [   62.492121]  ? tick_sched_do_timer+0x40/0x40
>>>   [   62.492121]  update_process_times+0x28/0x50
>>>   [   62.492121]  tick_sched_handle+0x22/0x70
>>>   [   62.492121]  tick_sched_timer+0x34/0x70
>>>   [   62.492121]  __hrtimer_run_queues+0xcc/0x250
>>>   [   62.492121]  hrtimer_interrupt+0xab/0x1f0
>>>   [   62.492121]  smp_apic_timer_interrupt+0x62/0x150
>>>   [   62.492121]  apic_timer_interrupt+0xa2/0xb0
>>>   [   62.492121]  </IRQ>
>>>   [   62.492121] RIP: 0010:iowrite16+0x1d/0x30
>>>   [   62.492121] RSP: 0018:ffffa477c034fcc8 EFLAGS: 00010292 ORIG_RAX: ffffffffffffff11
>>>   [   62.492121] RAX: ffffffffa24fbdb0 RBX: ffff92a1f8f82000 RCX: 0000000000000001
>>>   [   62.492121] RDX: ffffa477c0371000 RSI: ffffa477c0371000 RDI: 0000000000000000
>>>   [   62.492121] RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000001080020
>>>   [   62.492121] R10: ffffdc7cc1e4fc00 R11: 0000000000000000 R12: 0000000000000000
>>>   [   62.492121] R13: 0000000000000000 R14: ffff92a1f93f0000 R15: ffff92a1f8e1aa80
>>>   [   62.492121]  ? vp_synchronize_vectors+0x60/0x60
>>>   [   62.492121]  vp_notify+0x12/0x20
>>>   [   62.492121]  virtqueue_notify+0x18/0x30
>>>   [   62.492121]  virtio_queue_rq+0x2f5/0x300 [virtio_blk]
>>>   [   62.492121]  blk_mq_dispatch_rq_list+0x7e/0x4a0
>>>   [   62.492121]  blk_mq_do_dispatch_sched+0x4a/0xd0
>>>   [   62.492121]  blk_mq_sched_dispatch_requests+0x106/0x170
>>>   [   62.492121]  __blk_mq_run_hw_queue+0x80/0x90
>>>   [   62.492121]  process_one_work+0x1e3/0x420
>>>   [   62.492121]  worker_thread+0x2b/0x3d0
>>>   [   62.492121]  ? process_one_work+0x420/0x420
>>>   [   62.492121]  kthread+0x113/0x130
>>>   [   62.492121]  ? kthread_create_worker_on_cpu+0x50/0x50
>>>   [   62.492121]  ret_from_fork+0x3a/0x50
>>>
>>>   Another important thing is that the commit works well on other
>>>   hardware with the same setup (same host kernel, same qemu command line
>>>   and host kernel binaries). How could I try to find the issue reason?
>>>
>>> To manage notifications about this bug go to:
>>> https://bugs.launchpad.net/qemu/+bug/1750229/+subscriptions
>>
>>
>>
>> --
>> With best regards,
>> Matwey V. Kornilov
>
>
>
> --
> With best regards,
> Matwey V. Kornilov



-- 
With best regards,
Matwey V. Kornilov