Nina Schoetterl-Glausch <n...@linux.ibm.com> wrote:
> Hi,
>
> We're seeing failures running s390x migration kvm-unit-tests tests with TCG.
> Some initial findings:
> What seems to be happening is that after migration a control block header
> accessed by the test code is all zeros which causes an unexpected exception.
> I did a bisection which points to c8df4a7aef ("migration: Split
> save_live_pending() into state_pending_*") as the culprit.
> The migration issue persists after applying the fix e264705012 ("migration: I
> messed state_pending_exact/estimate") on top of c8df4a7aef.
>
> Applying
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 56ff9cd29d..2dc546cf28 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -3437,7 +3437,7 @@ static void ram_state_pending_exact(void *opaque,
> uint64_t max_size,
>
> uint64_t remaining_size = rs->migration_dirty_pages * TARGET_PAGE_SIZE;
>
> - if (!migration_in_postcopy()) {
> + if (!migration_in_postcopy() && remaining_size < max_size) {
> qemu_mutex_lock_iothread();
> WITH_RCU_READ_LOCK_GUARD() {
> migration_bitmap_sync_precopy(rs);
>
> on top fixes or hides the issue. (The comparison was removed by c8df4a7aef.)
> I arrived at this by experimentation, I haven't looked into why this makes a
> difference.
> Any thoughts on the matter appreciated.
This shouldn't be happening. Famous last words.
I am still applying the patch, to get back to old behaviour, but we
shouldn't be needing this.
Basically when we call ram_state_pending_exact() we know that we want to
sync the bitmap. But I guess that dirty block bitmap can be
"interesting" to say the less.
Later, Juan.
