[Qemu-devel] [PATCH v2 0/2] Block: don't do copy-on-read in before_write_notifier

[Wen Congyang]

If we do copy-on-read in before_write_notifier, qemu will be crashed. The
backtrace is:
Program terminated with signal 6, Aborted.
#0  0x00007f5d69207b55 in raise () from /lib64/libc.so.6
(gdb) bt
#0  0x00007f5d69207b55 in raise () from /lib64/libc.so.6
#1  0x00007f5d69209131 in abort () from /lib64/libc.so.6
#2  0x00007f5d69200a10 in __assert_fail () from /lib64/libc.so.6
#3  0x00007f5d6cb3a0d5 in wait_serialising_requests (self=0x7f5d36feeae0) at 
block/io.c:452
#4  0x00007f5d6cb3ae79 in bdrv_aligned_preadv (bs=0x7f5d6d570170, 
req=0x7f5d36feeae0, offset=93585408, bytes=65536, align=512, 
qiov=0x7f5d36feec90, flags=1)
    at block/io.c:847
#5  0x00007f5d6cb3b3cc in bdrv_co_do_preadv (bs=0x7f5d6d570170, 
offset=93585408, bytes=65536, qiov=0x7f5d36feec90, flags=BDRV_REQ_COPY_ON_READ)
    at block/io.c:971
#6  0x00007f5d6cb3b497 in bdrv_co_do_readv (bs=0x7f5d6d570170, 
sector_num=182784, nb_sectors=128, qiov=0x7f5d36feec90, flags=0) at 
block/io.c:993
#7  0x00007f5d6cb3b504 in bdrv_co_readv (bs=0x7f5d6d570170, sector_num=182784, 
nb_sectors=128, qiov=0x7f5d36feec90) at block/io.c:1002
#8  0x00007f5d6c8eaf42 in backup_do_cow (bs=0x7f5d6d570170, sector_num=182784, 
nb_sectors=8, error_is_read=0x0) at block/backup.c:132
#9  0x00007f5d6c8eb6cf in backup_before_write_notify (notifier=0x7f5d435fcf30, 
opaque=0x7f5d36feee40) at block/backup.c:193
#10 0x00007f5d6cb9ec33 in notifier_with_return_list_notify 
(list=0x7f5d6d5731f8, data=0x7f5d36feee40) at util/notify.c:65
#11 0x00007f5d6cb3bcc8 in bdrv_aligned_pwritev (bs=0x7f5d6d570170, 
req=0x7f5d36feee40, offset=93585408, bytes=4096, qiov=0x7f5d6eef4cf8, flags=0)
    at block/io.c:1126
#12 0x00007f5d6cb3c79e in bdrv_co_do_pwritev (bs=0x7f5d6d570170, 
offset=93585408, bytes=4096, qiov=0x7f5d6eef4cf8, flags=0) at block/io.c:1364
#13 0x00007f5d6cb3c867 in bdrv_co_do_writev (bs=0x7f5d6d570170, 
sector_num=182784, nb_sectors=8, qiov=0x7f5d6eef4cf8, flags=0) at 
block/io.c:1388
#14 0x00007f5d6cb3ea09 in bdrv_co_do_rw (opaque=0x7f5d38465ee0) at 
block/io.c:2123
#15 0x00007f5d6caeb03d in coroutine_trampoline (i0=944146112, i1=32605) at 
coroutine-ucontext.c:80
#16 0x00007f5d69218be0 in __correctly_grouped_prefixwc () from /lib64/libc.so.6
#17 0x0000000000000000 in ?? ()


Wen Congyang (2):
  block: Introduce a new API bdrv_co_no_copy_on_readv()
  Backup: don't do copy-on-read in before_write_notifier

 block/backup.c        | 20 ++++++++++++++------
 block/io.c            | 12 +++++++++++-
 include/block/block.h |  9 ++++++---
 trace-events          |  1 +
 4 files changed, 32 insertions(+), 10 deletions(-)

-- 
2.4.3