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

[Stefan Hajnoczi]

Maybe bdrv_snapshot_create() should take s->lock but it's not clear yet
what causes all qcow2 cache entries to be referenced.

How do you reproduce this crash?  Please give exact steps including what
commands to run inside the guest and what QEMU monitor commands to run.

Is the crash deterministic (does it happen every time or with a random
chance)?

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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".

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