[Bug 1923583] Re: colo: pvm flush failed after svm killed

[Thomas Huth]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting the bug state to "Incomplete" now.

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Thank you and sorry for the inconvenience.


** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1923583

Title:
  colo: pvm flush failed after svm killed

Status in QEMU:
  Incomplete

Bug description:
  Hi,
     Primary vm flush failed after killing svm, which leads primary vm guest 
filesystem unavailable.

  qemu versoin: 5.2.0
  host/guest os: CentOS Linux release 7.6.1810 (Core)

  Reproduce steps:
  1. create colo vm following 
https://github.com/qemu/qemu/blob/master/docs/COLO-FT.txt
  2. kill secondary vm (don't remove nbd child from quorum on primary vm)and 
wait for a minute. the interval depends on guest os.
  result: primary vm file system shutdown because of flush cache error.

  After serveral tests, I found that qemu-5.0.0 worked well, and it's
  the commit
  
https://git.qemu.org/?p=qemu.git;a=commit;h=883833e29cb800b4d92b5d4736252f4004885191(block:
  Flush all children in generic code) leads this change, and both
  virtio-blk and ide turned out to be bad.

  I think it's nbd(replication) flush failed leads bdrv_co_flush(quorum_bs) 
failed, here is the call stack.
  #0  bdrv_co_flush (bs=0x56242b3cc0b0=nbd_bs) at ../block/io.c:2856
  #1  0x0000562428b0f399 in bdrv_co_flush (bs=0x56242b3c7e00=replication_bs) at 
../block/io.c:2920
  #2  0x0000562428b0f399 in bdrv_co_flush (bs=0x56242a4ad800=quorum_bs) at 
../block/io.c:2920
  #3  0x0000562428b70d56 in blk_do_flush (blk=0x56242a4ad4a0) at 
../block/block-backend.c:1672
  #4  0x0000562428b70d87 in blk_aio_flush_entry (opaque=0x7fd0980073f0) at 
../block/block-backend.c:1680
  #5  0x0000562428c5f9a7 in coroutine_trampoline (i0=-1409269904, i1=32721) at 
../util/coroutine-ucontext.c:173

  While i am not sure whether i use colo inproperly? Can we assume that
  nbd child of quorum immediately removed right after svm crashed? Or
  it's really a bug? Does the following patch fix? Help is needed!
  Thanks a lot！

  diff --git a/block/quorum.c b/block/quorum.c
  index cfc1436..f2c0805 100644
  --- a/block/quorum.c
  +++ b/block/quorum.c
  @@ -1279,7 +1279,7 @@ static BlockDriver bdrv_quorum = {
       .bdrv_dirname                       = quorum_dirname,
       .bdrv_co_block_status               = quorum_co_block_status,
   
  -    .bdrv_co_flush_to_disk              = quorum_co_flush,
  +    .bdrv_co_flush                      = quorum_co_flush,
   
       .bdrv_getlength                     = quorum_getlength,

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