Just a quick follow-up, I can replicate it on 4.14.4 as well. More 
information, collected from the CentOS 7 domU the issue's been tested 
on:

cat /proc/version
Linux version 4.14.5-1.el7.elrepo.x86_64 (mockbuild@Build64R7) (gcc 
version 4.8.5 20150623 (Red Hat 4.8.5-16) (GCC)) #1 SMP Sun Dec 10 
09:54:56 EST 2017

cat /proc/cpuinfo
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 158
model name	: Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz
stepping	: 9
microcode	: 0x48
cpu MHz		: 3607.086
cache size	: 8192 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 1
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 22
wp		: yes
flags		: fpu de tsc msr pae cx8 apic sep cmov pat clflush mmx fxsr sse 
sse2 ss ht syscall nx lm constant_tsc rep_good nopl cpuid pni pclmulqdq 
ssse3 sdbg fma cx16 sse4_1 sse4_2 movbe popcnt tsc_deadline_timer aes 
xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch fsgsbase bmi1 
hle avx2 bmi2 erms rtm rdseed adx xsaveopt dtherm ida arat pln pts hwp 
hwp_notify hwp_act_window hwp_epp
bugs		:
bogomips	: 7214.02
clflush size	: 64
cache_alignment	: 64
address sizes	: 39 bits physical, 48 bits virtual
power management:

processor	: 1
vendor_id	: GenuineIntel
cpu family	: 6
model		: 158
model name	: Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz
stepping	: 9
microcode	: 0x48
cpu MHz		: 3607.086
cache size	: 8192 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 1
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 22
wp		: yes
flags		: fpu de tsc msr pae cx8 apic sep cmov pat clflush mmx fxsr sse 
sse2 ss ht syscall nx lm constant_tsc rep_good nopl cpuid pni pclmulqdq 
ssse3 sdbg fma cx16 sse4_1 sse4_2 movbe popcnt tsc_deadline_timer aes 
xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch fsgsbase bmi1 
hle avx2 bmi2 erms rtm rdseed adx xsaveopt dtherm ida arat pln pts hwp 
hwp_notify hwp_act_window hwp_epp
bugs		:
bogomips	: 7214.02
clflush size	: 64
cache_alignment	: 64
address sizes	: 39 bits physical, 48 bits virtual
power management:

awk -f scripts/ver_linux
If some fields are empty or look unusual you may have an old version.
Compare to the current minimal requirements in Documentation/Changes.

Linux adi7 4.14.5-1.el7.elrepo.x86_64 #1 SMP Sun Dec 10 09:54:56 EST 
2017 x86_64 x86_64 x86_64 GNU/Linux

GNU C               	4.8.5
GNU Make            	3.82
Binutils            	2.25.1
Util-linux          	2.23.2
Mount               	2.23.2
Module-init-tools   	20
E2fsprogs           	1.42.9
Xfsprogs            	4.5.0
Quota-tools         	4.01
PPP                 	2.4.5
Nfs-utils           	1.3.0
Linux C Library     	2.17
Dynamic linker (ldd)	2.17
Linux C++ Library   	6.0.19
Procps              	3.3.10
Net-tools           	2.10
Kbd                 	1.15.5
Console-tools       	1.15.5
Sh-utils            	8.22
Udev                	219
Modules Loaded      	aesni_intel auth_rpcgss coretemp crc32c_intel 
crc32_pclmul crct10dif_pclmul cryptd crypto_simd ext4 
ghash_clmulni_intel glue_helper grace intel_rapl_perf ip_set 
ip_set_hash_ip ip_tables jbd2 lockd mbcache nfnetlink nfs_acl nfsd pcbc 
pcspkr sunrpc x86_pkg_temp_thermal xen_blkfront xen_netfront

Kernel config attached.

Thanks,

---
Adi Pircalabu

On 12-12-2017 12:11, Adi Pircalabu wrote:

Hi, first of all, I'm not subscribed to the linux-block@ list. Running
"xl -v vcpu-set <domU> <val>" in Dom0 triggers the warning below, then
a number of commands like top or ls stall. The only domU recovery
solution is to terminate it immediately using "xl destroy".

I couldn't replicate it on:
- CentOS 6 running kernel-2.6.32-696.16.1.el6.x86_64,
kernel-lt-4.4.105-1.el6.elrepo.x86_64
- CentOS 7 running 4.9.67-1.el7.centos.x86_64

But I can replicate it consistently on:
- CentOS 6 running 4.14.5-1.el6.elrepo.x86_64
- CentOS 7 running 4.14.5-1.el7.elrepo.x86_64

dom0 versions tested with similar results in the domU:
- 4.6.6-6.el7 on kernel 4.9.63-29.el7.x86_64
- 4.6.3-15.el6 on kernel 4.9.37-29.el6.x86_64

Noticed behaviour:
- These commands stall:
top
ls -l /var/tmp
ls -l /tmp
- Stuck in D state on the CentOS 7 domU:
root         5  0.0  0.0      0     0 ?        D    11:20   0:00 
[kworker/u8:0]
root       316  0.0  0.0      0     0 ?        D    11:20   0:00 
[jbd2/xvda1-8]
root      1145  0.0  0.2 116636  4776 ?        Ds   11:20   0:00 -bash
root      1289  0.0  0.1  25852  2420 ?        Ds   11:35   0:00
/usr/bin/systemd-tmpfiles --clean
root      1290  0.0  0.1 125248  2696 pts/1    D+   11:44   0:00 ls
--color=auto -l /tmp/
root      1293  0.0  0.1 125248  2568 pts/2    D+   11:44   0:00 ls
--color=auto -l /var/tmp
root      1296  0.0  0.2 116636  4908 pts/3    Ds+  11:44   0:00 -bash
root      1358  0.0  0.1 125248  2612 pts/4    D+   11:47   0:00 ls
--color=auto -l /var/tmp

At a first glance it appears the issue is the domU kernel. Stack traces 
follow:

-----CentOS 6 kernel-ml-4.14.5-1.el6.elrepo.x86_64 start here-----
------------[ cut here ]------------
WARNING: CPU: 4 PID: 60 at block/blk-mq.c:1144 
__blk_mq_run_hw_queue+0x9e/0xc0
Modules linked in: intel_cstate(-) ipt_REJECT nf_reject_ipv4
nf_conntrack_ipv4 nf_defrag_ipv4 xt_multiport iptable_filter ip_tables
ip6t_REJECT nf_reject_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 xt_state
nf_conntrack libcrc32c ip6table_filter ip6_tables dm_mod dax
xen_netfront crc32_pclmul crct10dif_pclmul ghash_clmulni_intel
crc32c_intel pcbc aesni_intel glue_helper crypto_simd cryptd
aes_x86_64 coretemp hwmon x86_pkg_temp_thermal sb_edac intel_rapl_perf
pcspkr ext4 jbd2 mbcache xen_blkfront
CPU: 4 PID: 60 Comm: kworker/4:1H Not tainted 
4.14.5-1.el6.elrepo.x86_64 #1
Workqueue: kblockd blk_mq_run_work_fn
task: ffff8802711a2780 task.stack: ffffc90041af4000
RIP: e030:__blk_mq_run_hw_queue+0x9e/0xc0
RSP: e02b:ffffc90041af7c48 EFLAGS: 00010202
RAX: 0000000000000001 RBX: ffff88027117fa80 RCX: 0000000000000001
RDX: ffff88026b053ee0 RSI: ffff88027351bca0 RDI: ffff88026b072800
RBP: ffffc90041af7c68 R08: ffffc90041af7eb8 R09: ffff8802711a2810
R10: 0000000000007ff0 R11: 0000000000000001 R12: ffff88026b072800
R13: ffffe8ffffd04d00 R14: 0000000000000000 R15: ffffe8ffffd04d05
FS:  00002b7b7c89b700(0000) GS:ffff880273500000(0000) 
knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 000000026d953000 CR4: 0000000000042660
Call Trace:
 blk_mq_run_work_fn+0x31/0x40
 process_one_work+0x174/0x440
 ? xen_mc_flush+0xad/0x1b0
 ? schedule+0x3a/0xa0
 worker_thread+0x6b/0x410
 ? default_wake_function+0x12/0x20
 ? __wake_up_common+0x84/0x130
 ? maybe_create_worker+0x120/0x120
 ? schedule+0x3a/0xa0
 ? _raw_spin_unlock_irqrestore+0x16/0x20
 ? maybe_create_worker+0x120/0x120
 kthread+0x111/0x150
 ? __kthread_init_worker+0x40/0x40
 ret_from_fork+0x25/0x30
Code: 89 df e8 06 2f d9 ff 4c 89 e7 41 89 c5 e8 0b 6e 00 00 44 89 ee
48 89 df e8 20 2f d9 ff 48 8b 5d e8 4c 8b 65 f0 4c 8b 6d f8 c9 c3 <0f>
ff eb aa 4c 89 e7 e8 e6 6d 00 00 48 8b 5d e8 4c 8b 65 f0 4c
---[ end trace fe2aaf4e723042fd ]---
-----CentOS 6 kernel-ml-4.14.5-1.el6.elrepo.x86_64 end here-----

-----CentOS 7 kernel-ml-4.14.5-1.el7.elrepo.x86_64 start here-----
[  116.528885] ------------[ cut here ]------------
[  116.528894] WARNING: CPU: 3 PID: 38 at block/blk-mq.c:1144
__blk_mq_run_hw_queue+0x89/0xa0
[  116.528898] Modules linked in: intel_cstate(-) ip_set_hash_ip
ip_set nfnetlink x86_pkg_temp_thermal coretemp crct10dif_pclmul
crc32_pclmul ghash_clmulni_intel pcbc aesni_intel crypto_simd
glue_helper cryptd intel_rapl_perf pcspkr nfsd auth_rpcgss nfs_acl
lockd grace sunrpc ip_tables ext4 mbcache jbd2 xen_netfront
xen_blkfront crc32c_intel
[  116.528919] CPU: 3 PID: 38 Comm: kworker/3:1H Not tainted
4.14.5-1.el7.elrepo.x86_64 #1
[  116.529007] Code: 00 e8 7c c5 45 00 4c 89 e7 e8 14 4b d7 ff 48 89
df 41 89 c5 e8 19 66 00 00 44 89 ee 4c 89 e7 e8 2e 4b d7 ff 5b 41 5c
41 5d 5d c3 <0f> ff eb b4 48 89 df e8 fb 65 00 00 5b 41 5c 41 5d 5d c3
0f ff
[  116.529034] ---[ end trace a7814e3ec9a330c6 ]---
[  147.424117] ------------[ cut here ]------------
[  147.424150] WARNING: CPU: 2 PID: 24 at block/blk-mq.c:1144
__blk_mq_run_hw_queue+0x89/0xa0
[  147.424160] Modules linked in: ip_set_hash_ip ip_set nfnetlink
x86_pkg_temp_thermal coretemp crct10dif_pclmul crc32_pclmul
ghash_clmulni_intel pcbc aesni_intel crypto_simd glue_helper cryptd
intel_rapl_perf pcspkr nfsd auth_rpcgss nfs_acl lockd grace sunrpc
ip_tables ext4 mbcache jbd2 xen_netfront xen_blkfront crc32c_intel
[  147.424222] CPU: 2 PID: 24 Comm: kworker/2:0H Tainted: G        W
    4.14.5-1.el7.elrepo.x86_64 #1
[  147.424238] Workqueue: kblockd blk_mq_run_work_fn
[  147.424247] task: ffff88007c539840 task.stack: ffffc900403e4000
[  147.424259] RIP: e030:__blk_mq_run_hw_queue+0x89/0xa0
[  147.424270] RSP: e02b:ffffc900403e7e30 EFLAGS: 00010202
[  147.424279] RAX: 0000000000000001 RBX: ffff880003b83800 RCX: 
ffff88007d11bca0
[  147.424288] RDX: ffff88007c656c88 RSI: 00000000000000a0 RDI: 
ffff880003b83800
[  147.424298] RBP: ffffc900403e7e48 R08: 0000000000000000 R09: 
0000000000000000
[  147.424309] R10: 0000000000007ff0 R11: 00000000000074e5 R12: 
ffff88007c436900
[  147.424319] R13: ffff88007d11bc80 R14: ffff88007d121b00 R15: 
ffff880003b83848
[  147.424340] FS:  0000000000000000(0000) GS:ffff88007d100000(0000)
knlGS:ffff88007d100000
[  147.424350] CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
[  147.424359] CR2: 00007f504f19a700 CR3: 0000000079bed000 CR4: 
0000000000042660
[  147.424370] Call Trace:
[  147.424384]  blk_mq_run_work_fn+0x2c/0x30
[  147.424400]  process_one_work+0x149/0x360
[  147.424411]  worker_thread+0x4d/0x3e0
[  147.424421]  kthread+0x109/0x140
[  147.424432]  ? rescuer_thread+0x380/0x380
[  147.424441]  ? kthread_park+0x60/0x60
[  147.424455]  ret_from_fork+0x25/0x30
[  147.424463] Code: 00 e8 7c c5 45 00 4c 89 e7 e8 14 4b d7 ff 48 89
df 41 89 c5 e8 19 66 00 00 44 89 ee 4c 89 e7 e8 2e 4b d7 ff 5b 41 5c
41 5d 5d c3 <0f> ff eb b4 48 89 df e8 fb 65 00 00 5b 41 5c 41 5d 5d c3
0f ff
[  147.424554] ---[ end trace a7814e3ec9a330c7 ]---
-----CentOS 7 kernel-ml-4.14.5-1.el7.elrepo.x86_64 end here-----