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Re: QEMU migration-test CI intermittent failure
From: |
Peter Xu |
Subject: |
Re: QEMU migration-test CI intermittent failure |
Date: |
Thu, 14 Sep 2023 19:27:28 -0400 |
On Thu, Sep 14, 2023 at 07:54:17PM -0300, Fabiano Rosas wrote:
> Fabiano Rosas <farosas@suse.de> writes:
>
> > Peter Xu <peterx@redhat.com> writes:
> >
> >> On Thu, Sep 14, 2023 at 12:57:08PM -0300, Fabiano Rosas wrote:
> >>> I managed to reproduce it. It's not the return path error. In hindsight
> >>> that's obvious because that error happens in the 'recovery' test and this
> >>> one in the 'plain' one. Sorry about the noise.
> >>
> >> No worry. It's good to finally identify that.
> >>
> >>>
> >>> This one reproduced with just 4 iterations of preempt/plain. I'll
> >>> investigate.
> >
> > It seems that we're getting a tcp disconnect (ECONNRESET) on when doing
> > that shutdown() on postcopy_qemufile_src. The one from commit 6621883f93
> > ("migration: Fix potential race on postcopy_qemufile_src").
> >
> > I'm trying to determine why that happens when other times it just
> > returns 0 as expected.
> >
> > Could this mean that we're kicking the dest too soon while it is still
> > receiving valid data?
>
> Looking a bit more into this, what's happening is that
> postcopy_ram_incoming_cleanup() is shutting the postcopy_qemufile_dst
> while ram_load_postcopy() is still running.
>
> The postcopy_ram_listen_thread() function waits for the
> main_thread_load_event, but that only works when not using preempt. With
> the preempt thread, the event is set right away and we proceed to do the
> cleanup without waiting.
>
> So the assumption of commit 6621883f93 that the incoming side knows when
> it has finished migrating is wrong IMO. Without the EOS we're relying on
> the chance that the shutdown() happens after the last recvmsg has
> returned and not during it.
>
> Peter, what do you think?
That's a good point.
One thing to verify that (sorry, I still cannot reproduce it myself, which
is so weirdly... it seems loads won't really help reproducing this) is to
let the main thread wait for all requested pages to arrive:
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 29aea9456d..df055c51ea 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -597,6 +597,12 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState
*mis)
trace_postcopy_ram_incoming_cleanup_entry();
if (mis->preempt_thread_status == PREEMPT_THREAD_CREATED) {
+ /*
+ * NOTE! it's possible that the preempt thread is still handling
+ * the last pages to arrive which were requested by faults. Making
+ * sure nothing is left behind.
+ */
+ while (qatomic_read(&mis->page_requested_count));
/* Notify the fast load thread to quit */
mis->preempt_thread_status = PREEMPT_THREAD_QUIT;
if (mis->postcopy_qemufile_dst) {
If that can work solidly, we can figure out a better way than a dead loop
here.
Thanks,
--
Peter Xu
- QEMU migration-test CI intermittent failure, Stefan Hajnoczi, 2023/09/13
- Re: QEMU migration-test CI intermittent failure, Fabiano Rosas, 2023/09/13
- Re: QEMU migration-test CI intermittent failure, Stefan Hajnoczi, 2023/09/13
- Re: QEMU migration-test CI intermittent failure, Peter Xu, 2023/09/14
- Re: QEMU migration-test CI intermittent failure, Fabiano Rosas, 2023/09/14
- Re: QEMU migration-test CI intermittent failure, Peter Xu, 2023/09/14
- Re: QEMU migration-test CI intermittent failure, Fabiano Rosas, 2023/09/14
- Re: QEMU migration-test CI intermittent failure, Peter Xu, 2023/09/14
- Re: QEMU migration-test CI intermittent failure, Fabiano Rosas, 2023/09/14
- Re: QEMU migration-test CI intermittent failure, Fabiano Rosas, 2023/09/14
- Re: QEMU migration-test CI intermittent failure,
Peter Xu <=
- Re: QEMU migration-test CI intermittent failure, Fabiano Rosas, 2023/09/14
- Re: QEMU migration-test CI intermittent failure, Peter Xu, 2023/09/15
- Re: QEMU migration-test CI intermittent failure, Peter Xu, 2023/09/15
- Re: QEMU migration-test CI intermittent failure, Fabiano Rosas, 2023/09/18
- Re: QEMU migration-test CI intermittent failure, Peter Xu, 2023/09/18