Linux Virtualization - May 2019 - [Qemu-devel] [PATCH v9 2/7] virtio-pmem: Add virtio pmem driver

On 5/14/19 7:54 AM, Pankaj Gupta wrote:
> +		if (!list_empty(&vpmem->req_list)) {
> +			req_buf = list_first_entry(&vpmem->req_list,
> +					struct virtio_pmem_request, list);
> +			req_buf->wq_buf_avail = true;
> +			wake_up(&req_buf->wq_buf);
> +			list_del(&req_buf->list);
Yes, this change is the right one, thank you!
> +	 /*
> +	  * If virtqueue_add_sgs returns -ENOSPC then req_vq virtual
> +	  * queue does not have free descriptor. We add the request
> +	  * to req_list and wait for host_ack to wake us up when free
> +	  * slots are available.
> +	  */
> +	while ((err = virtqueue_add_sgs(vpmem->req_vq, sgs, 1, 1, req,
> +					GFP_ATOMIC)) == -ENOSPC) {
> +
> +		dev_err(&vdev->dev, "failed to send command to virtio
pmem" \
> +			"device, no free slots in the virtqueue\n");
> +		req->wq_buf_avail = false;
> +		list_add_tail(&req->list, &vpmem->req_list);
> +		spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> +
> +		/* A host response results in "host_ack" getting called */
> +		wait_event(req->wq_buf, req->wq_buf_avail);
> +		spin_lock_irqsave(&vpmem->pmem_lock, flags);
> +	}
> +	err1 = virtqueue_kick(vpmem->req_vq);
> +	spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> +
> +	/*
> +	 * virtqueue_add_sgs failed with error different than -ENOSPC, we
can't
> +	 * do anything about that.
> +	 */
> +	if (err || !err1) {
> +		dev_info(&vdev->dev, "failed to send command to virtio pmem
device\n");
> +		err = -EIO;
> +	} else {
> +		/* A host repsonse results in "host_ack" getting called */
> +		wait_event(req->host_acked, req->done);
> +		err = req->ret;
> +I confirm that the failures I was facing with the `-ENOSPC` error path are
not present in v9.
Best,
Jakub Staron

Hi Jakub,
> 
> On 5/14/19 7:54 AM, Pankaj Gupta wrote:
> > +		if (!list_empty(&vpmem->req_list)) {
> > +			req_buf = list_first_entry(&vpmem->req_list,
> > +					struct virtio_pmem_request, list);
> > +			req_buf->wq_buf_avail = true;
> > +			wake_up(&req_buf->wq_buf);
> > +			list_del(&req_buf->list);
> Yes, this change is the right one, thank you!
Thank you for the confirmation.
> 
> > +	 /*
> > +	  * If virtqueue_add_sgs returns -ENOSPC then req_vq virtual
> > +	  * queue does not have free descriptor. We add the request
> > +	  * to req_list and wait for host_ack to wake us up when free
> > +	  * slots are available.
> > +	  */
> > +	while ((err = virtqueue_add_sgs(vpmem->req_vq, sgs, 1, 1, req,
> > +					GFP_ATOMIC)) == -ENOSPC) {
> > +
> > +		dev_err(&vdev->dev, "failed to send command to virtio
pmem" \
> > +			"device, no free slots in the virtqueue\n");
> > +		req->wq_buf_avail = false;
> > +		list_add_tail(&req->list, &vpmem->req_list);
> > +		spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> > +
> > +		/* A host response results in "host_ack" getting called
*/
> > +		wait_event(req->wq_buf, req->wq_buf_avail);
> > +		spin_lock_irqsave(&vpmem->pmem_lock, flags);
> > +	}
> > +	err1 = virtqueue_kick(vpmem->req_vq);
> > +	spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> > +
> > +	/*
> > +	 * virtqueue_add_sgs failed with error different than -ENOSPC, we
can't
> > +	 * do anything about that.
> > +	 */
> > +	if (err || !err1) {
> > +		dev_info(&vdev->dev, "failed to send command to virtio
pmem device\n");
> > +		err = -EIO;
> > +	} else {
> > +		/* A host repsonse results in "host_ack" getting called
*/
> > +		wait_event(req->host_acked, req->done);
> > +		err = req->ret;
> > +I confirm that the failures I was facing with the `-ENOSPC` error
path are
> > not present in v9.
Can I take it your reviewed/acked-by? or tested-by tag? for the virtio patch :)

Thank you,
Pankaj
> 
> Best,
> Jakub Staron
> 
>

On 5/16/19 10:35 PM, Pankaj Gupta wrote:
> Can I take it your reviewed/acked-by? or tested-by tag? for the virtio
patch :)I don't feel that I have enough expertise to give the reviewed-by
tag, but you can
take my acked-by + tested-by.

Acked-by: Jakub Staron <jstaron at google.com>
Tested-by: Jakub Staron <jstaron at google.com>

No kernel panics/stalls encountered during testing this patches (v9) with QEMU +
xfstests.
Some CPU stalls encountered while testing with crosvm instead of QEMU with
xfstests
(test generic/464) but no repro for QEMU, so the fault may be on the side of
crosvm.


The dump for the crosvm/xfstests stall:
[ 2504.175276] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[ 2504.176681] rcu:     0-...!: (1 GPs behind) idle=9b2/1/0x4000000000000000
softirq=1089198/1089202 fqs=0
[ 2504.178270] rcu:     2-...!: (1 ticks this GP) idle=cfe/1/0x4000000000000002
softirq=1055108/1055110 fqs=0
[ 2504.179802] rcu:     3-...!: (1 GPs behind) idle=1d6/1/0x4000000000000002
softirq=1046798/1046802 fqs=0
[ 2504.181215] rcu:     4-...!: (2 ticks this GP) idle=522/1/0x4000000000000002
softirq=1249063/1249064 fqs=0
[ 2504.182625] rcu:     5-...!: (1 GPs behind) idle=6da/1/0x4000000000000000
softirq=1131036/1131047 fqs=0
[ 2504.183955]  (detected by 3, t=0 jiffies, g=1232529, q=1370)
[ 2504.184762] Sending NMI from CPU 3 to CPUs 0:
[ 2504.186400] NMI backtrace for cpu 0
[ 2504.186401] CPU: 0 PID: 6670 Comm: 464 Not tainted 5.1.0+ #1
[ 2504.186401] Hardware name: ChromiumOS crosvm, BIOS 0 
[ 2504.186402] RIP: 0010:queued_spin_lock_slowpath+0x1c/0x1e0
[ 2504.186402] Code: e7 89 c8 f0 44 0f b1 07 39 c1 75 dc f3 c3 0f 1f 44 00 00 ba
01 00 00 00 8b 07 85 c0 75 0a f0 0f b1 17 85 c0 75 f2 f3 c3 f3 90 <eb> ec
81 fe 00 01 00 00 0f 84 ab 00 00 00 81 e6 00 ff ff ff 75 44
[ 2504.186403] RSP: 0018:ffffc90000003ee8 EFLAGS: 00000002
[ 2504.186404] RAX: 0000000000000001 RBX: 0000000000000246 RCX: 0000000000404044
[ 2504.186404] RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffffffff8244a280
[ 2504.186405] RBP: ffffffff8244a280 R08: 00000000000f4200 R09: 0000024709ed6c32
[ 2504.186405] R10: 0000000000000000 R11: 0000000000000001 R12: ffffffff8244a280
[ 2504.186405] R13: 0000000000000009 R14: 0000000000000009 R15: 0000000000000000
[ 2504.186406] FS:  0000000000000000(0000) GS:ffff8880cc600000(0000)
knlGS:0000000000000000
[ 2504.186406] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2504.186406] CR2: 00007efd6b0f15d8 CR3: 000000000260a006 CR4: 0000000000360ef0
[ 2504.186407] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 2504.186407] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 2504.186407] Call Trace:
[ 2504.186408]  <IRQ>
[ 2504.186408]  _raw_spin_lock_irqsave+0x1d/0x30
[ 2504.186408]  rcu_core+0x3b6/0x740
[ 2504.186408]  ? __hrtimer_run_queues+0x133/0x280
[ 2504.186409]  ? recalibrate_cpu_khz+0x10/0x10
[ 2504.186409]  __do_softirq+0xd8/0x2e4
[ 2504.186409]  irq_exit+0xa3/0xb0
[ 2504.186410]  smp_apic_timer_interrupt+0x67/0x120
[ 2504.186410]  apic_timer_interrupt+0xf/0x20
[ 2504.186410]  </IRQ>
[ 2504.186410] RIP: 0010:unmap_page_range+0x47a/0x9b0
[ 2504.186411] Code: 0f 46 46 10 49 39 6e 18 49 89 46 10 48 89 e8 49 0f 43 46 18
41 80 4e 20 08 4d 85 c9 49 89 46 18 0f 84 68 ff ff ff 49 8b 51 08 <48> 8d
42 ff 83 e2 01 49 0f 44 c1 f6 40 18 01 75 38 48 ba ff 0f 00
[ 2504.186411] RSP: 0018:ffffc900036cbcc8 EFLAGS: 00000282 ORIG_RAX:
ffffffffffffff13
[ 2504.186412] RAX: ffffffffffffffff RBX: 800000003751d045 RCX: 0000000000000001
[ 2504.186413] RDX: ffffea0002e09288 RSI: 000000000269b000 RDI: ffff8880b6525e40
[ 2504.186413] RBP: 000000000269c000 R08: 0000000000000000 R09: ffffea0000dd4740
[ 2504.186413] R10: ffffea0001755700 R11: ffff8880cc62d120 R12: 0000000002794000
[ 2504.186414] R13: 000000000269b000 R14: ffffc900036cbdf0 R15: ffff8880572434d8
[ 2504.186414]  ? unmap_page_range+0x420/0x9b0
[ 2504.186414]  ? release_pages+0x175/0x390
[ 2504.186414]  unmap_vmas+0x7c/0xe0
[ 2504.186415]  exit_mmap+0xa4/0x190
[ 2504.186415]  mmput+0x3b/0x100
[ 2504.186415]  do_exit+0x276/0xc10
[ 2504.186415]  do_group_exit+0x35/0xa0
[ 2504.186415]  __x64_sys_exit_group+0xf/0x10
[ 2504.186416]  do_syscall_64+0x43/0x120
[ 2504.186416]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 2504.186416] RIP: 0033:0x7efd6ae10618
[ 2504.186416] Code: Bad RIP value.
[ 2504.186417] RSP: 002b:00007ffcac9bde38 EFLAGS: 00000246 ORIG_RAX:
00000000000000e7
[ 2504.186417] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007efd6ae10618
[ 2504.186418] RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
[ 2504.186418] RBP: 00007efd6b0ed8e0 R08: 00000000000000e7 R09: ffffffffffffff98
[ 2504.186418] R10: 00007ffcac9bddb8 R11: 0000000000000246 R12: 00007efd6b0ed8e0
[ 2504.186419] R13: 00007efd6b0f2c20 R14: 0000000000000060 R15: 000000000070e705
[ 2504.186421] NMI backtrace for cpu 3
[ 2504.226980] CPU: 3 PID: 6596 Comm: xfs_io Not tainted 5.1.0+ #1
[ 2504.227661] Hardware name: ChromiumOS crosvm, BIOS 0 
[ 2504.228261] Call Trace:
[ 2504.228552]  <IRQ>
[ 2504.228795]  dump_stack+0x46/0x5b
[ 2504.229180]  nmi_cpu_backtrace+0x89/0x90
[ 2504.229649]  ? lapic_can_unplug_cpu+0x90/0x90
[ 2504.230157]  nmi_trigger_cpumask_backtrace+0x82/0xc0
[ 2504.230751]  rcu_dump_cpu_stacks+0x8b/0xb7
[ 2504.231222]  rcu_sched_clock_irq+0x6f6/0x720
[ 2504.231726]  ? tick_sched_do_timer+0x50/0x50
[ 2504.232214]  update_process_times+0x23/0x50
[ 2504.232693]  tick_sched_handle+0x2f/0x40
[ 2504.233144]  tick_sched_timer+0x32/0x70
[ 2504.233594]  __hrtimer_run_queues+0x103/0x280
[ 2504.234092]  hrtimer_interrupt+0xe0/0x240
[ 2504.234580]  smp_apic_timer_interrupt+0x5d/0x120
[ 2504.235152]  apic_timer_interrupt+0xf/0x20
[ 2504.235627]  </IRQ>
[ 2504.235879] RIP: 0010:__memcpy_flushcache+0x4b/0x180
[ 2504.236452] Code: 8d 5d e0 4c 8d 62 20 48 89 f7 48 29 d7 48 89 d9 48 83 e1 e0
4c 01 e1 48 8d 04 17 4c 8b 02 4c 8b 4a 08 4c 8b 52 10 4c 8b 5a 18 <4c> 0f
c3 00 4c 0f c3 48 08 4c 0f c3 50 10 4c 0f c3 58 18 48 83 c2
[ 2504.238592] RSP: 0018:ffffc90003ae38e8 EFLAGS: 00010286 ORIG_RAX:
ffffffffffffff13
[ 2504.239467] RAX: ffff888341800000 RBX: 0000000000000fe0 RCX: ffff88801bd22000
[ 2504.240277] RDX: ffff88801bd21000 RSI: ffff888341800000 RDI: 0000000325adf000
[ 2504.241092] RBP: 0000000000001000 R08: cdcdcdcdcdcdcdcd R09: cdcdcdcdcdcdcdcd
[ 2504.241908] R10: cdcdcdcdcdcdcdcd R11: cdcdcdcdcdcdcdcd R12: ffff88801bd21020
[ 2504.242751] R13: ffff8880b916b600 R14: ffff888341800000 R15: ffffea00006f4840
[ 2504.243602]  write_pmem+0x61/0x90
[ 2504.244002]  pmem_do_bvec+0x178/0x2c0
[ 2504.244469]  ? chksum_update+0xe/0x20
[ 2504.244908]  pmem_make_request+0xf7/0x270
[ 2504.245509]  generic_make_request+0x199/0x3f0
[ 2504.246179]  ? submit_bio+0x67/0x130
[ 2504.246710]  submit_bio+0x67/0x130
[ 2504.247117]  ext4_io_submit+0x44/0x50
[ 2504.247556]  ext4_writepages+0x621/0xe80
[ 2504.248028]  ? 0xffffffff81000000
[ 2504.248418]  ? do_writepages+0x46/0xd0
[ 2504.248880]  ? ext4_mark_inode_dirty+0x1d0/0x1d0
[ 2504.249417]  do_writepages+0x46/0xd0
[ 2504.249833]  ? release_pages+0x175/0x390
[ 2504.250290]  ? __filemap_fdatawrite_range+0x7c/0xb0
[ 2504.250879]  __filemap_fdatawrite_range+0x7c/0xb0
[ 2504.251427]  ext4_release_file+0x67/0xa0
[ 2504.251897]  __fput+0xb1/0x220
[ 2504.252260]  task_work_run+0x79/0xa0
[ 2504.252676]  do_exit+0x2ca/0xc10
[ 2504.253063]  ? __switch_to_asm+0x40/0x70
[ 2504.253530]  ? __switch_to_asm+0x34/0x70
[ 2504.253995]  ? __switch_to_asm+0x40/0x70
[ 2504.254446]  do_group_exit+0x35/0xa0
[ 2504.254865]  get_signal+0x14e/0x7a0
[ 2504.255281]  ? __switch_to_asm+0x34/0x70
[ 2504.255749]  ? __switch_to_asm+0x40/0x70
[ 2504.256224]  do_signal+0x2b/0x5e0
[ 2504.256619]  ? __switch_to_asm+0x40/0x70
[ 2504.257086]  ? __switch_to_asm+0x34/0x70
[ 2504.257552]  ? __switch_to_asm+0x40/0x70
[ 2504.258022]  ? __switch_to_asm+0x34/0x70
[ 2504.258488]  ? __schedule+0x253/0x530
[ 2504.258943]  ? __switch_to_asm+0x34/0x70
[ 2504.259398]  exit_to_usermode_loop+0x87/0xa0
[ 2504.259900]  do_syscall_64+0xf7/0x120
[ 2504.260326]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 2504.260923] RIP: 0033:0x7faf347e28bd
[ 2504.261348] Code: Bad RIP value.
[ 2504.261727] RSP: 002b:00007faf33fc5f40 EFLAGS: 00000293 ORIG_RAX:
0000000000000022
[ 2504.262594] RAX: fffffffffffffdfe RBX: 0000000000000000 RCX: 00007faf347e28bd
[ 2504.263416] RDX: 8b9da1f4246cdb38 RSI: 0000000000000000 RDI: 0000000000000000
[ 2504.264215] RBP: 0000000000000000 R08: 00007faf33fc6700 R09: 00007faf33fc6700
[ 2504.265061] R10: 000000000000012d R11: 0000000000000293 R12: 00007ffdf142327e
[ 2504.266082] R13: 00007ffdf142327f R14: 00007faf337c6000 R15: 0000000000000003

Arch: x86_64
Kernel: stable top with virtio-pmem v9 patches applied
Distro: Debian Stretch

But as I said, it may be just a problem with crosvm.


Thank you,
Jakub Staron