[Qemu-devel] [Bug 1401798] Re: Qemu 2.2.0 savevm crash.

[changlimin]

I think I get the reason.

>From Qemu 2.2.0, in qcow2_open:  l2_cache_size = 
>MAX(DEFAULT_L2_CACHE_BYTE_SIZE/s->cluster_size, MIN_L2_CACHE_SIZE);
Here DEFAULT_L2_CACHE_BYTE_SIZE=1M, MIN_L2_CACHE_SIZE=1.

If the cluster_size < 1M, the  l2_cache_size will be greater than 1, it
is ok.

If the cluster_size>=1M, the l2_cache_size will be 1. After create
snapshot, the first qcow2_co_writev will abort at
qcow2_cache_find_entry_to_replace, because no free room in
l2_table_cache. If change the MIN_L2_CACHE_SIZE to 16, it is ok.

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1401798

Title:
  Qemu 2.2.0 savevm crash.

Status in QEMU:
  New

Bug description:
  qemu 2.1.2 is good.

  (gdb) bt
  #0  0x00007ffff4aae445 in raise () from /lib/x86_64-linux-gnu/libc.so.6
  #1  0x00007ffff4ab1bab in abort () from /lib/x86_64-linux-gnu/libc.so.6
  #2  0x0000555555997951 in qcow2_cache_find_entry_to_replace 
(c=0x555556389780) at block/qcow2-cache.c:262
  #3  0x0000555555997a1a in qcow2_cache_do_get (bs=0x5555563836f0, 
c=0x555556389780, offset=1094713344, table=0x7fffffffc528, 
      read_from_disk=true) at block/qcow2-cache.c:285
  #4  0x0000555555997c45 in qcow2_cache_get (bs=0x5555563836f0, 
c=0x555556389780, offset=1094713344, table=0x7fffffffc528)
      at block/qcow2-cache.c:331
  #5  0x0000555555991ca9 in l2_allocate (bs=0x5555563836f0, l1_index=1, 
table=0x7fffffffc5a0) at block/qcow2-cluster.c:247
  #6  0x000055555599290c in get_cluster_table (bs=0x5555563836f0, 
offset=549755813888, new_l2_table=0x7fffffffc610, 
      new_l2_index=0x7fffffffc62c) at block/qcow2-cluster.c:620
  #7  0x0000555555994213 in discard_single_l2 (bs=0x5555563836f0, 
offset=549755813888, nb_clusters=156, type=QCOW2_DISCARD_NEVER, 
      full_discard=false) at block/qcow2-cluster.c:1425
  #8  0x0000555555994491 in qcow2_discard_clusters (bs=0x5555563836f0, 
offset=549755813888, nb_sectors=638976, type=QCOW2_DISCARD_NEVER, 
      full_discard=false) at block/qcow2-cluster.c:1516
  #9  0x00005555559965c8 in qcow2_snapshot_create (bs=0x5555563836f0, 
sn_info=0x7fffffffc830) at block/qcow2-snapshot.c:441
  #10 0x00005555559ad1ad in bdrv_snapshot_create (bs=0x5555563836f0, 
sn_info=0x7fffffffc830) at block/snapshot.c:167
  #11 0x000055555565e90f in do_savevm (mon=0x555556992d20, 
qdict=0x5555599d5c00) at /vms/qemu/qemu-2.2.0/savevm.c:1126

  (gdb) show args
  Argument list to give program being debugged when it is started is "-name 
u1404-01 -S -machine pc,accel=kvm,usb=off -m 1024 -smp 
2,sockets=2,cores=1,threads=1 -no-user-config -nodefaults -monitor stdio -rtc 
base=utc -no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 
-device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5 -drive 
file=/vms/images/u1404-01.img,if=none,id=drive-virtio-disk0,format=qcow2,cache=directsync
 -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0
 -drive if=none,id=drive-ide0-1-0,readonly=on,format=raw -device 
ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -chardev 
pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -device 
usb-tablet,id=input0 -vnc 0.0.0.0:0 -device 
cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device 
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6".

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1401798/+subscriptions