@@ -252,9 +252,8 @@ static int multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
p->packet_num = be64_to_cpu(packet->packet_num);
p->packets_recved++;
- if (!(p->flags & MULTIFD_FLAG_SYNC)) {
- ret = multifd_ram_unfill_packet(p, errp);
- }
+ /* Always unfill, old QEMUs (<9.0) send data along with SYNC */
+ ret = multifd_ram_unfill_packet(p, errp);
trace_multifd_recv_unfill(p->id, p->packet_num, p->flags,
p->next_packet_size);
@@ -1156,9 +1155,13 @@ static void *multifd_recv_thread(void *opaque)
flags = p->flags;
/* recv methods don't know how to handle the SYNC flag */
p->flags &= ~MULTIFD_FLAG_SYNC;
- if (!(flags & MULTIFD_FLAG_SYNC)) {
- has_data = p->normal_num || p->zero_num;
- }
+
+ /*
+ * Even if it's a SYNC packet, this needs to be set
+ * because older QEMUs (<9.0) still send data along with
+ * the SYNC packet.
+ */
+ has_data = p->normal_num || p->zero_num;
qemu_mutex_unlock(&p->mutex);
} else {
/*
Commit f5f48a7891 ("migration/multifd: Separate SYNC request with normal jobs") changed the multifd source side to stop sending data along with the MULTIFD_FLAG_SYNC, effectively introducing the concept of a SYNC-only packet. Relying on that, commit d7e58f412c ("migration/multifd: Don't send ram data during SYNC") later came along and skipped reading data from SYNC packets. In a versions timeline like this: 8.2 f5f48a7 9.0 9.1 d7e58f41 9.2 The issue arises that QEMUs < 9.0 still send data along with SYNC, but QEMUs > 9.1 don't gather that data anymore. This leads to various kinds of migration failures due to desync/missing data. Stop checking for a SYNC packet on the destination and unconditionally unfill the packet. >From now on: old -> new: the source sends data + sync, destination reads normally new -> new: source sends only sync, destination reads zeros new -> old: source sends only sync, destination reads zeros CC: qemu-stable@nongnu.org Fixes: d7e58f412c ("migration/multifd: Don't send ram data during SYNC") Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2720 Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Fabiano Rosas <farosas@suse.de> Message-Id: <20241213160120.23880-2-farosas@suse.de> Signed-off-by: Fabiano Rosas <farosas@suse.de> --- migration/multifd.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)