When the problem occurs, iostat -xk shows the following:
avg-cpu: %user %nice %system %iowait %steal %idle
0.00 0.00 0.25 24.94 0.00 74.81
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s
avgrq-sz avgqu-sz await r_await w_await svctm %util
vda 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.00
vdb 0.00 0.00 0.00 0.00 0.00 0.00
0.00 1.00 0.00 0.00 0.00 0.00 100.00
Backtrace from all threads on the qemu process:
(gdb) thread apply all bt
Thread 7 (Thread 0x7f25e65ff700 (LWP 4428)):
#0 0x00007f25ff2ba17f in pthread_cond_wait@@GLIBC_2.3.2 ()
from /lib/x86_64-linux-gnu/libpthread.so.0
#1 0x0000560da8d5b359 in qemu_cond_wait ()
#2 0x0000560da8cadd0b in ?? ()
#3 0x0000560da8cae258 in ?? ()
#4 0x00007f25ff2b44a4 in start_thread ()
from /lib/x86_64-linux-gnu/libpthread.so.0
#5 0x00007f25feff6d0f in clone () from /lib/x86_64-linux-gnu/libc.so.6
Thread 6 (Thread 0x7f25e7fff700 (LWP 4426)):
#0 0x00007f25fefef017 in ioctl () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x0000560da8a0a4b7 in kvm_vcpu_ioctl ()
#2 0x0000560da8a0a610 in kvm_cpu_exec ()
#3 0x0000560da89f8138 in ?? ()
#4 0x00007f25ff2b44a4 in start_thread ()
from /lib/x86_64-linux-gnu/libpthread.so.0
#5 0x00007f25feff6d0f in clone () from /lib/x86_64-linux-gnu/libc.so.6
Thread 5 (Thread 0x7f25f4a2c700 (LWP 4425)):
#0 0x00007f25fefef017 in ioctl () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x0000560da8a0a4b7 in kvm_vcpu_ioctl ()
#2 0x0000560da8a0a610 in kvm_cpu_exec ()
#3 0x0000560da89f8138 in ?? ()
#4 0x00007f25ff2b44a4 in start_thread ()
from /lib/x86_64-linux-gnu/libpthread.so.0
#5 0x00007f25feff6d0f in clone () from /lib/x86_64-linux-gnu/libc.so.6
Thread 4 (Thread 0x7f25f522d700 (LWP 4424)):
#0 0x00007f25fefef017 in ioctl () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x0000560da8a0a4b7 in kvm_vcpu_ioctl ()
#2 0x0000560da8a0a610 in kvm_cpu_exec ()
#3 0x0000560da89f8138 in ?? ()
#4 0x00007f25ff2b44a4 in start_thread ()
from /lib/x86_64-linux-gnu/libpthread.so.0
#5 0x00007f25feff6d0f in clone () from /lib/x86_64-linux-gnu/libc.so.6
Thread 3 (Thread 0x7f25f5a2e700 (LWP 4423)):
#0 0x00007f25fefef017 in ioctl () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x0000560da8a0a4b7 in kvm_vcpu_ioctl ()
#2 0x0000560da8a0a610 in kvm_cpu_exec ()
#3 0x0000560da89f8138 in ?? ()
#4 0x00007f25ff2b44a4 in start_thread ()
from /lib/x86_64-linux-gnu/libpthread.so.0
#5 0x00007f25feff6d0f in clone () from /lib/x86_64-linux-gnu/libc.so.6
Thread 2 (Thread 0x7f25f6c32700 (LWP 4387)):
#0 0x00007f25feff2469 in syscall () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x0000560da8d5b668 in qemu_event_wait ()
#2 0x0000560da8d6a94e in ?? ()
#3 0x00007f25ff2b44a4 in start_thread ()
from /lib/x86_64-linux-gnu/libpthread.so.0
#4 0x00007f25feff6d0f in clone () from /lib/x86_64-linux-gnu/libc.so.6
Thread 1 (Thread 0x7f2604776c80 (LWP 4386)):
#0 0x00007f25fefed981 in ppoll () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x0000560da8cbd359 in qemu_poll_ns ()
#2 0x0000560da8cbcd6a in main_loop_wait ()
#3 0x0000560da89be1ed in main ()
(gdb) info thread
Id Target Id Frame
* 1 Thread 0x7f2604776c80 (LWP 4386) "GUEST" 0x00007f25fefed981 in
ppoll ()
from /lib/x86_64-linux-gnu/libc.so.6
2 Thread 0x7f25f6c32700 (LWP 4387) "qemu-system-x86"
0x00007f25feff2469 in syscall () from /lib/x86_64-linux-gnu/libc.so.6
3 Thread 0x7f25f5a2e700 (LWP 4423) "GUEST" 0x00007f25fefef017 in
ioctl ()
from /lib/x86_64-linux-gnu/libc.so.6
4 Thread 0x7f25f522d700 (LWP 4424) "GUEST" 0x00007f25fefef017 in
ioctl ()
from /lib/x86_64-linux-gnu/libc.so.6
5 Thread 0x7f25f4a2c700 (LWP 4425) "GUEST" 0x00007f25fefef017 in
ioctl ()
from /lib/x86_64-linux-gnu/libc.so.6
6 Thread 0x7f25e7fff700 (LWP 4426) "GUEST" 0x00007f25fefef017 in
ioctl ()
from /lib/x86_64-linux-gnu/libc.so.6
7 Thread 0x7f25e65ff700 (LWP 4428) "GUEST" 0x00007f25ff2ba17f in
pthread_cond_wait@@GLIBC_2.3.2 () from /lib/x86_64-linux-gnu/libpthread.so.0
