Re: [Qemu-devel] [PATCH] iothread: Stop threads before main() quits

[Fam Zheng <famz@redhat.com>]

On Tue, 09/13 09:39, Stefan Hajnoczi wrote:
> On Thu, Sep 08, 2016 at 05:28:51PM +0800, Fam Zheng wrote:
> > Right after main_loop ends, we release various things but keep iothread
> > alive. The latter is not prepared to the sudden change of resources.
> > 
> > Specifically, after bdrv_close_all(), virtio-scsi dataplane get a
> > surprise at the empty BlockBackend:
> > 
> > (gdb) bt
> >     at /usr/src/debug/qemu-2.6.0/hw/scsi/virtio-scsi.c:543
> >     at /usr/src/debug/qemu-2.6.0/hw/scsi/virtio-scsi.c:577
> > 
> > It is because the d->conf.blk->root is set to NULL, then
> > blk_get_aio_context() returns qemu_aio_context, whereas s->ctx is still
> > pointing to the iothread:
> > 
> >     hw/scsi/virtio-scsi.c:543:
> > 
> >     if (s->dataplane_started) {
> >         assert(blk_get_aio_context(d->conf.blk) == s->ctx);
> >     }
> > 
> > To fix this, let's stop iothreads before doing bdrv_close_all().
> 
> Did you consider blk_add_remove_bs_notifier()?  It gets called during
> bdrv_close_all() and would let virtio-scsi survive any other case where
> the same thing happens.

There is already another case (eject):

https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg02243.html

And I don't know how to fix it with blk_add_remove_bs_notifier. Could you
elaborate?

Fam