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virtio-balloon: always indicate S_DONE when migration fails 

If something goes wrong during precopy, before stopping the VM, we will
never send a S_DONE indication to the VM, resulting in the hinted pages
not getting released to be used by the guest OS (e.g., Linux).

Easy to reproduce:
1. Start migration (e.g., HMP "migrate -d 'exec:gzip -c > STATEFILE.gz'")
2. Cancel migration (e.g., HMP "migrate_cancel")
3. Oberve in the guest (e.g., cat /proc/meminfo) that there is basically
   no free memory left.

While at it, add similar locking to virtio_balloon_free_page_done() as
done in virtio_balloon_free_page_stop. Locking is still weird, but that
has to be sorted out separately.

There is nothing to do in the PRECOPY_NOTIFY_COMPLETE case. Add some
comments regarding S_DONE handling.

Fixes: c13c4153f7 ("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT")
Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Wei Wang <wei.w.wang@intel.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200629080615.26022-1-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
David Hildenbrand 2020-06-29 10:06:15 +02:00 committed by Michael S. Tsirkin
parent 0d935ffd66
commit dd8eeb9671
1 changed files with 20 additions and 6 deletions
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26
hw/virtio/virtio-balloon.c
View File

@ -628,8 +628,13 @@ static void virtio_balloon_free_page_done(VirtIOBalloon *s)
{
VirtIODevice *vdev = VIRTIO_DEVICE(s);
s->free_page_report_status = FREE_PAGE_REPORT_S_DONE;
virtio_notify_config(vdev);
if (s->free_page_report_status != FREE_PAGE_REPORT_S_DONE) {
/* See virtio_balloon_free_page_stop() */
qemu_mutex_lock(&s->free_page_lock);
s->free_page_report_status = FREE_PAGE_REPORT_S_DONE;
qemu_mutex_unlock(&s->free_page_lock);
virtio_notify_config(vdev);
}
}
static int
@ -653,17 +658,26 @@ virtio_balloon_free_page_report_notify(NotifierWithReturn *n, void *data)
case PRECOPY_NOTIFY_SETUP:
precopy_enable_free_page_optimization();
break;
case PRECOPY_NOTIFY_COMPLETE:
case PRECOPY_NOTIFY_CLEANUP:
case PRECOPY_NOTIFY_BEFORE_BITMAP_SYNC:
virtio_balloon_free_page_stop(dev);
break;
case PRECOPY_NOTIFY_AFTER_BITMAP_SYNC:
if (vdev->vm_running) {
virtio_balloon_free_page_start(dev);
} else {
virtio_balloon_free_page_done(dev);
break;
}
/*
* Set S_DONE before migrating the vmstate, so the guest will reuse
* all hinted pages once running on the destination. Fall through.
*/
case PRECOPY_NOTIFY_CLEANUP:
/*
* Especially, if something goes wrong during precopy or if migration
* is canceled, we have to properly communicate S_DONE to the VM.
*/
virtio_balloon_free_page_done(dev);
break;
case PRECOPY_NOTIFY_COMPLETE:
break;
default:
virtio_error(vdev, "%s: %d reason unknown", __func__, pnd->reason);