Hi, recently one of our users provided a backtrace[0] for the following assertion failure during a live migration that uses drive-mirror to sync a local disk: > bdrv_co_write_req_prepare: Assertion `!(bs->open_flags & BDRV_O_INACTIVE)' > failed
The way we do migration with a local disk is essentially: 1. start target instance with a suitable NBD export 2. start drive-mirror on the source side and wait for it to become ready once 3. issue 'migrate' QMP command 4. cancel drive-mirror blockjob after the migration has finished I reproduced the issue with the following fio script running in the guest (to dirty lots of clusters): > fio --name=make-mirror-work --size=100M --direct=1 --rw=randwrite \ > --bs=4k --ioengine=psync --numjobs=5 --runtime=60 --time_based AFAIU, the issue is that nothing guarantees that the drive mirror is ready when the migration inactivates the block drives. Is using copy-mode=write-blocking for drive-mirror to only way to avoid this issue? There, the downside is that the network (used by the mirror) would become a bottleneck for IO in the guest, while the behavior would really only be needed during the final phase. I guess the assert should be avoided in any case. Here's a few ideas that came to mind: 1. migration should fail gracefully 2. migration should wait for the mirror-jobs to become ready before inactivating the block drives - that would increase the downtime in these situations of course 2A. additionally, drive-mirror could be taken into account when converging the migration somehow? I noticed the following comment in the mirror implementation > /* Note that even when no rate limit is applied we need to yield > * periodically with no pending I/O so that bdrv_drain_all() returns. > * We do so every BLKOCK_JOB_SLICE_TIME nanoseconds, or when there is > * an error, or when the source is clean, whichever comes first. */ 3. change draining behavior after the job was ready once, so that bdrv_drain_all() will only return when the job is ready again? Hope I'm not completely misunderstanding this. Best Regards, Fiona [0]: > Thread 1 (Thread 0x7f3389d4a000 (LWP 2297576) "kvm"): > #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50 > #1 0x00007f339488d537 in __GI_abort () at abort.c:79 > #2 0x00007f339488d40f in __assert_fail_base (fmt=0x7f3394a056a8 "%s%s%s:%u: > %s%sAssertion `%s' failed.\n%n", assertion=0x5595f85bfd70 "!(bs->open_flags & > BDRV_O_INACTIVE)", file=0x5595f85cb576 "../block/io.c", line=2026, > function=<optimized out>) at assert.c:92 > #3 0x00007f339489c662 in __GI___assert_fail > (assertion=assertion@entry=0x5595f85bfd70 "!(bs->open_flags & > BDRV_O_INACTIVE)", file=file@entry=0x5595f85cb576 "../block/io.c", > line=line@entry=2026, function=function@entry=0x5595f85cc510 > <__PRETTY_FUNCTION__.8> "bdrv_co_write_req_prepare") at assert.c:101 > #4 0x00005595f83218f2 in bdrv_co_write_req_prepare (child=0x5595f91cab90, > offset=60867018752, bytes=196608, req=0x7f324a2e9d70, flags=0) at > ../block/io.c:2026 > #5 0x00005595f8323384 in bdrv_aligned_pwritev > (child=child@entry=0x5595f91cab90, req=req@entry=0x7f324a2e9d70, > offset=60867018752, bytes=196608, align=align@entry=1, qiov=0x5595f9030d58, > qiov_offset=0, flags=0) at ../block/io.c:2140 > #6 0x00005595f832485a in bdrv_co_pwritev_part (child=0x5595f91cab90, > offset=<optimized out>, offset@entry=60867018752, bytes=<optimized out>, > bytes@entry=196608, qiov=<optimized out>, qiov@entry=0x5595f9030d58, > qiov_offset=<optimized out>, qiov_offset@entry=0, flags=flags@entry=0) at > ../block/io.c:2353 > #7 0x00005595f8315a09 in blk_co_do_pwritev_part > (blk=blk@entry=0x5595f91db8c0, offset=60867018752, bytes=196608, > qiov=qiov@entry=0x5595f9030d58, qiov_offset=qiov_offset@entry=0, > flags=flags@entry=0) at ../block/block-backend.c:1365 > #8 0x00005595f8315bdd in blk_co_pwritev_part (flags=0, qiov_offset=0, > qiov=qiov@entry=0x5595f9030d58, bytes=<optimized out>, offset=<optimized > out>, blk=0x5595f91db8c0) at ../block/block-backend.c:1380 > #9 blk_co_pwritev (blk=0x5595f91db8c0, offset=<optimized out>, > bytes=<optimized out>, qiov=qiov@entry=0x5595f9030d58, flags=flags@entry=0) > at ../block/block-backend.c:1391 > #10 0x00005595f8328a59 in mirror_read_complete (ret=0, op=0x5595f9030d50) at > ../block/mirror.c:260 > #11 mirror_co_read (opaque=0x5595f9030d50) at ../block/mirror.c:400 > #12 0x00005595f843a39b in coroutine_trampoline (i0=<optimized out>, > i1=<optimized out>) at ../util/coroutine-ucontext.c:177 > #13 0x00007f33948b8d40 in ?? () from /lib/x86_64-linux-gnu/libc.so.6 > #14 0x00007f324a3ea6e0 in ?? () > #15 0x0000000000000000 in ?? ()
