repeated the assert in #26:
Program received signal SIGABRT, Aborted.
0x00007f02163005f7 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56	  return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig);
(gdb) where
#0  0x00007f02163005f7 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007f0216301ce8 in __GI_abort () at abort.c:90
#2  0x00007f02162f9566 in __assert_fail_base (fmt=0x7f0216449288 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x560ac0191e93 "!ioc->write_coroutine", file=file@entry=0x560ac0191e66 "/root/qemu/io/channel.c", line=line@entry=303, function=function@entry=0x560ac0191f60 <__PRETTY_FUNCTION__.22239> "qio_channel_yield")
    at assert.c:92
#3  0x00007f02162f9612 in __GI___assert_fail (assertion=assertion@entry=0x560ac0191e93 "!ioc->write_coroutine", file=file@entry=0x560ac0191e66 "/root/qemu/io/channel.c", line=line@entry=303, function=function@entry=0x560ac0191f60 <__PRETTY_FUNCTION__.22239> "qio_channel_yield") at assert.c:101
#4  0x0000560ac0036a08 in qio_channel_yield (ioc=ioc@entry=0x560ac2397c90, condition=condition@entry=G_IO_OUT)
    at /root/qemu/io/channel.c:303
#5  0x0000560ac001930e in nbd_rwv (ioc=0x560ac2397c90, iov=<optimized out>, niov=<optimized out>, length=<optimized out>, do_read=do_read@entry=false, errp=errp@entry=0x0) at /root/qemu/nbd/common.c:47
#6  0x0000560ac0007e24 in nbd_co_send_request (bs=bs@entry=0x560ac30167a0, request=request@entry=0x7f0209afc9a0, qiov=qiov@entry=0x560ac2428d68) at /root/qemu/block/nbd-client.c:154
#7  0x0000560ac0008244 in nbd_client_co_pwritev (bs=0x560ac30167a0, offset=3414163456, bytes=<optimized out>, qiov=0x560ac2428d68, flags=<optimized out>) at /root/qemu/block/nbd-client.c:260
#8  0x0000560ac00030e1 in bdrv_driver_pwritev (bs=bs@entry=0x560ac30167a0, offset=offset@entry=3414163456, bytes=bytes@entry=589824, qiov=qiov@entry=0x560ac2428d68, flags=flags@entry=0) at /root/qemu/block/io.c:877
#9  0x0000560ac0004480 in bdrv_aligned_pwritev (req=req@entry=0x7f0209afcba0, offset=offset@entry=3414163456, bytes=589824, align=align@entry=1, qiov=qiov@entry=0x560ac2428d68, flags=flags@entry=0, child=0x560ac1f0a9b0, child=0x560ac1f0a9b0) at /root/qemu/block/io.c:1382
#10 0x0000560ac0005258 in bdrv_co_pwritev (child=0x560ac1f0a9b0, offset=offset@entry=3414163456, bytes=<optimized out>, qiov=qiov@entry=0x560ac2428d68, flags=0) at /root/qemu/block/io.c:1633
#11 0x0000560abffbf564 in raw_co_pwritev (bs=0x560ac22807f0, offset=3414163456, bytes=<optimized out>, qiov=0x560ac2428d68, flags=<optimized out>) at /root/qemu/block/raw-format.c:243
#12 0x0000560ac00030e1 in bdrv_driver_pwritev (bs=bs@entry=0x560ac22807f0, offset=offset@entry=3414163456, bytes=bytes@entry=589824, qiov=qiov@entry=0x560ac2428d68, flags=flags@entry=0) at /root/qemu/block/io.c:877
#13 0x0000560ac0004480 in bdrv_aligned_pwritev (req=req@entry=0x7f0209afce70, offset=offset@entry=3414163456, bytes=589824, align=align@entry=1, qiov=qiov@entry=0x560ac2428d68, flags=flags@entry=0, child=0x560ac33c1e70, child=0x560ac33c1e70) at /root/qemu/block/io.c:1382
#14 0x0000560ac0005258 in bdrv_co_pwritev (child=0x560ac33c1e70, offset=offset@entry=3414163456, bytes=<optimized out>, bytes@entry=589824, qiov=qiov@entry=0x560ac2428d68, flags=0) at /root/qemu/block/io.c:1633
#15 0x0000560abfff5173 in blk_co_pwritev (blk=0x560ac14f31e0, offset=3414163456, bytes=589824, qiov=0x560ac2428d68, flags=<optimized out>) at /root/qemu/block/block-backend.c:1062
#16 0x0000560abfff528a in blk_aio_write_entry (opaque=0x560ac2c18f70) at /root/qemu/block/block-backend.c:1253
#17 0x0000560ac0092cca in coroutine_trampoline (i0=<optimized out>, i1=<optimized out>)
    at /root/qemu/util/coroutine-ucontext.c:79
#18 0x00007f0216312110 in __start_context () at /lib64/libc.so.6
#19 0x00007fff12c4db30 in  ()
#20 0x0000000000000000 in  ()
(gdb)