On 29.06.20 16:18, Vladimir Sementsov-Ogievskiy wrote: > 29.06.2020 16:48, Max Reitz wrote: >> Hi, >> >> In an iotest, I’m trying to quit qemu immediately after a migration has >> failed. Unfortunately, that doesn’t seem to be possible in a clean way: >> migrate_fd_cleanup() runs only at some point after the migration state >> is already “failed”, so if I just wait for that “failed” state and >> immediately quit, some cleanup functions may not have been run yet. >> >> This is a problem with dirty bitmap migration at least, because it >> increases the refcount on all block devices that are to be migrated, so >> if we don’t call the cleanup function before quitting, the refcount will >> stay elevated and bdrv_close_all() will hit an assertion because those >> block devices are still around after blk_remove_all_bs() and >> blockdev_close_all_bdrv_states(). >> >> In practice this particular issue might not be that big of a problem, >> because it just means qemu aborts when the user intended to let it quit >> anyway. But on one hand I could imagine that there are other clean-up >> paths that should definitely run before qemu quits (although I don’t >> know), and on the other, it’s a problem for my test. >> >> I tried working around the problem for my test by waiting on “Unable to >> write” appearing on stderr, because that indicates that >> migrate_fd_cleanup()’s error_report_err() has been reached. But on one >> hand, that isn’t really nice, and on the other, it doesn’t even work >> when the failure is on the source side (because then there is no >> s->error for migrate_fd_cleanup() to report).
(I’ve now managed to work around it by invoking blockdev-del on a node
affected by bitmap migration until it succeeds, because blockdev-del can
only succeed once the bitmap migration code has dropped its reference to
it.)
>> In all, I’m asking:
>> (1) Is there a nice solution for me now to delay quitting qemu until the
>> failed migration has been fully resolved, including the clean-up?
>>
>> (2) Isn’t it a problem if qemu crashes when you issue “quit” via QMP at
>> the wrong time? Like, maybe lingering subprocesses when using “exec”?
>>
>>
>
> I'll look more closely tomorrow, but as a short answer: try my series
> "[PATCH v2 00/22] Fix error handling during bitmap postcopy" it
> handles different problems around migration failures & qemu shutdown,
> probably it will help.
Not, it doesn’t seem to.
I’m not sure what exactly that series addresses, but FWIW I’m hitting
the problem in non-postcopy migration. What my simplest reproducer does is:
On the source VM:
blockdev-add node-name='foo' driver='null-co'
block-dirty-bitmap-add node='foo' name='bmap0'
(Launch destination VM with some -incoming, e.g.
-incoming 'exec: cat /tmp/mig_file')
Both on source and destination:
migrate-set-capabilities capabilities=[
{capability='events', state=true},
{capability='dirty-bitmaps', state=true}
]
On source:
migrate uri='exec: cat > /tmp/mig_file'
Then wait for a MIGRATION event with data/status == 'failed', and then
issue 'quit'.
Max
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