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

[Jeff Cody]

On Tue, Sep 08, 2015 at 11:28:31AM +0800, Wen Congyang wrote:
> 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
>

Thanks, applied to my block branch:

git://github.com/codyprime/qemu-kvm-jtc.git block

-Jeff