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[Qemu-devel] [Bug 1396052] Re: migration failed when running BurnInTest

From: z08687
Subject: [Qemu-devel] [Bug 1396052] Re: migration failed when running BurnInTest in guest
Date: Sat, 26 May 2018 13:35:22 -0000

I think the bug is still there. And I have repaired it myself.  
Migration process need wait all nbd-flying-data completion before 
bdrv_invalidate_cache_all was called.  The solution is working well but not 
graceful,so I didn't commit to open source community.

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  migration failed when running BurnInTest in guest

Status in QEMU:

Bug description:
  I found a live migration problem and have found out the reason, but I can't 
fix it up myself. I really need help.
  When live migration vm and it's block device in save time, it will occur 
probabilistic .

  1.  start a windows vm,and run burnInTest(it will write dirty data to block 
device in migration)
  2.  migrate vm with it's block device.
  3.  a few minutes later,  dest vm was killed and migration will be failed 
(probabilistic )

      when migraion start, in source host libvirt will send command to qemu,and 
qemu will call mirror_run coroutine to copy blcok device data to dest vm block 
device.    mirror_run running in qemu main thread.   When this 
finished(actually it still running because in following steps,there may 
generate dirty data by vm), qemu will  start migration_thread to migration ram 
and other device.
      In dest vm, qemu will call "bdrv_invalidate_cache --> 
qcow2_invalidate_cache" function after vm read "QEMU_VM_EOF" byte. 
qcow2_invalidate_cache fuction call qcow2_close ,  in qcow2_close fuction set 
"s->l1_table = NULL" and then call qcow2_cache_flush fuction.   In 
qcow2_cache_flush fuction will call 
This will let itself back to mian loop.   If source vm send block device dirty 
data to dest vm at this time, in dest vm will occur the following segmentation 
      The primary reason is mirror_run and migration run in two thread.  
although qemu stopping vm before write "QEMU_VM_EOF" byte, it still can't 
ensure mirror_run coroutine do not write dirty data  after migration thread  
sending "QEMU_VM_EOF" byte.

  Program received signal SIGSEGV, Segmentation fault.
  0x00007f90d250db24 in get_cluster_table (bs=0x7f90d493f500, 
offset=1832189952, new_l2_table=0x7f8fbd6faa88, 
      new_l2_index=0x7f8fbd6faaa0) at block/qcow2-cluster.c:573
  573         l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
  (gdb) bt
  #0  0x00007f90d250db24 in get_cluster_table (bs=0x7f90d493f500, 
offset=1832189952, new_l2_table=0x7f8fbd6faa88, 
      new_l2_index=0x7f8fbd6faaa0) at block/qcow2-cluster.c:573
  #1  0x00007f90d250e577 in handle_copied (bs=0x7f90d493f500, 
guest_offset=1832189952, host_offset=0x7f8fbd6fab18, 
      bytes=0x7f8fbd6fab20, m=0x7f8fbd6fabc8) at block/qcow2-cluster.c:927
  #2  0x00007f90d250ef45 in qcow2_alloc_cluster_offset (bs=0x7f90d493f500, 
offset=1832189952, num=0x7f8fbd6fabfc, 
      host_offset=0x7f8fbd6fabc0, m=0x7f8fbd6fabc8) at 
  #3  0x00007f90d250445f in qcow2_co_writev (bs=0x7f90d493f500, 
sector_num=3578496, remaining_sectors=2040, 
      qiov=0x7f8fbd6fae90) at block/qcow2.c:1171
  #4  0x00007f90d24d4764 in bdrv_aligned_pwritev (bs=0x7f90d493f500, 
req=0x7f8fbd6facd0, offset=1832189952, bytes=1044480, 
      qiov=0x7f8fbd6fae90, flags=0) at block.c:3321
  #5  0x00007f90d24d4d21 in bdrv_co_do_pwritev (bs=0x7f90d493f500, 
offset=1832189952, bytes=1044480, qiov=0x7f8fbd6fae90, 
      flags=0) at block.c:3447
  #6  0x00007f90d24d3115 in bdrv_rw_co_entry (opaque=0x7f8fbd6fae10) at 
  #7  0x00007f90d24d31e7 in bdrv_prwv_co (bs=0x7f90d493f500, offset=1832189952, 
qiov=0x7f8fbd6fae90, is_write=true, flags=0)
      at block.c:2746
  #8  0x00007f90d24d32eb in bdrv_rw_co (bs=0x7f90d493f500, sector_num=3578496, 
 <incomplete sequence \313>..., nb_sectors=2040, is_write=true, flags=0) at 
  #9  0x00007f90d24d3429 in bdrv_write (bs=0x7f90d493f500, sector_num=3578496, 
 <incomplete sequence \313>..., nb_sectors=2040) at block.c:2810
  #10 0x00007f90d24cc2b5 in nbd_trip (opaque=0x7f90d4ba9aa0) at nbd.c:1191
  #11 0x00007f90d24e86fb in coroutine_trampoline (i0=-725586416, i1=32656) at 
  #12 0x00007f90d0449310 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
  #13 0x00007fff3fcfda10 in ?? ()
  #14 0x0000000000000000 in ?? ()
  (gdb) p bs
  $1 = (BlockDriverState *) 0x7f90d493f500
  (gdb) p *s
  $3 = {cluster_bits = 16, cluster_size = 65536, cluster_sectors = 128, l2_bits 
= 13, l2_size = 8192, l1_size = 40, 
    l1_vm_state_index = 40, csize_shift = 54, csize_mask = 255, 
cluster_offset_mask = 18014398509481983, 
    l1_table_offset = 196608, l1_table = 0x0, l2_table_cache = 0x7f90d493eee0, 
refcount_block_cache = 0x7f90d493ef30, 
    cluster_cache = 0x7f90d4a84350 "", cluster_data = 0x7f90ce4de010 "", 
cluster_cache_offset = 18446744073709551615, 
    cluster_allocs = {lh_first = 0x0}, refcount_table = 0x7f90d4a94360, 
refcount_table_offset = 65536, 
    refcount_table_size = 8192, free_cluster_index = 209420, free_byte_offset = 
0, lock = {locked = true, queue = {entries = {
          tqh_first = 0x0, tqh_last = 0x7f90d4942c60}}}, crypt_method = 0, 
crypt_method_header = 0, aes_encrypt_key = {
      rd_key = {0 <repeats 60 times>}, rounds = 0}, aes_decrypt_key = {rd_key = 
{0 <repeats 60 times>}, rounds = 0}, 
    snapshots_offset = 0, snapshots_size = 0, nb_snapshots = 0, snapshots = 
0x0, flags = 10338, qcow_version = 3, 
    use_lazy_refcounts = false, refcount_order = 4, discard_passthrough = 
{false, true, false, true, false}, 
    overlap_check = 127, incompatible_features = 0, compatible_features = 0, 
autoclear_features = 0, 
    unknown_header_fields_size = 0, unknown_header_fields = 0x0, 
unknown_header_ext = {lh_first = 0x0}, discards = {
      tqh_first = 0x0, tqh_last = 0x7f90d4942ec8}, cache_discards = false}
  (gdb) p s->l1_table
  $4 = (uint64_t *) 0x0

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