Re: QEMU assert (was: [xen-unstable test] 181558: regressions - FAIL)

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Tue, Jul 04, 2023 at 11:56:54AM +0200, Roger Pau Monné wrote:
> On Tue, Jul 04, 2023 at 10:37:38AM +0100, Anthony PERARD wrote:
> > On Wed, Jun 28, 2023 at 02:31:39PM +0200, Roger Pau Monné wrote:
> > > On Fri, Jun 23, 2023 at 03:04:21PM +0000, osstest service owner wrote:
> > > > flight 181558 xen-unstable real [real]
> > > > http://logs.test-lab.xenproject.org/osstest/logs/181558/
> > > > 
> > > > Regressions :-(
> > > > 
> > > > Tests which did not succeed and are blocking,
> > > > including tests which could not be run:
> > > >  test-amd64-amd64-xl-qcow2   21 guest-start/debian.repeat fail REGR. 
> > > > vs. 181545
> > > 
> > > The test failing here is hitting the assert in qemu_cond_signal() as
> > > called by worker_thread():
> > > 
> > > #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
> > > #1  0x00007ffff740b535 in __GI_abort () at abort.c:79
> > > #2  0x00007ffff740b40f in __assert_fail_base (fmt=0x7ffff756cef0 
> > > "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=0x55555614abcb 
> > > "cond->initialized",
> > >     file=0x55555614ab88 
> > > "../qemu-xen-dir-remote/util/qemu-thread-posix.c", line=198, 
> > > function=<optimized out>) at assert.c:92
> > > #3  0x00007ffff74191a2 in __GI___assert_fail (assertion=0x55555614abcb 
> > > "cond->initialized", file=0x55555614ab88 
> > > "../qemu-xen-dir-remote/util/qemu-thread-posix.c", line=198,
> > >     function=0x55555614ad80 <__PRETTY_FUNCTION__.17104> 
> > > "qemu_cond_signal") at assert.c:101
> > > #4  0x0000555555f1c8d2 in qemu_cond_signal (cond=0x7fffb800db30) at 
> > > ../qemu-xen-dir-remote/util/qemu-thread-posix.c:198
> > > #5  0x0000555555f36973 in worker_thread (opaque=0x7fffb800dab0) at 
> > > ../qemu-xen-dir-remote/util/thread-pool.c:129
> > > #6  0x0000555555f1d1d2 in qemu_thread_start (args=0x7fffb8000b20) at 
> > > ../qemu-xen-dir-remote/util/qemu-thread-posix.c:505
> > > #7  0x00007ffff75b0fa3 in start_thread (arg=<optimized out>) at 
> > > pthread_create.c:486
> > > #8  0x00007ffff74e206f in clone () at 
> > > ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
> > > 
> > > I've been trying to figure out how it can get in such state, but so
> > > far I had no luck.  I'm not a QEMU expert, so it's probably better if
> > > someone else could handle this.
> > > 
> > > In the failures I've seen, and the reproduction I have, the assert
> > > triggers in the QEMU dom0 instance responsible for locally-attaching
> > > the disk to dom0 in order to run pygrub.
> > > 
> > > This is also with QEMU 7.2, as testing with upstream QEMU is blocked
> > > ATM, so there's a chance it has already been fixed upstream.
> > > 
> > > Thanks, Roger.
> > 
> > So, I've run a test with the latest QEMU and I can still reproduce the
> > issue. The test also fails with QEMU 7.1.0.
> > 
> > But, QEMU 7.0 seems to pass the test, even with a start-stop loop of 200
> > iteration. So I'll try to find out if something change in that range.
> > Or try to find out why would the thread pool be not initialised
> > properly.
> 
> Thanks for looking into this.
> 
> There are a set of changes from Paolo Bonzini:
> 
> 232e9255478f thread-pool: remove stopping variable
> 900fa208f506 thread-pool: replace semaphore with condition variable
> 3c7b72ddca9c thread-pool: optimize scheduling of completion bottom half
> 
> That landed in 7.1 that seem like possible candidates.

I think I've figured out the issue. I've sent a patch:
https://lore.kernel.org/qemu-devel/20230714152720.5077-1-anthony.perard@xxxxxxxxxx/

I did run osstest with this patch, and 200 iteration of stop/start, no
more issue of qemu for dom0 disapearing. The issue I've found is osstest
not able to ssh to the guest, which seems to be started. And qemu for
dom0 is still running.

While the report exist:
    http://logs.test-lab.xenproject.org/osstest/logs/181785/

Cheers,

-- 
Anthony PERARD