| Message ID | 20241213160120.23880-2-farosas@suse.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | migration: Fix regressions | expand |
On Fri, Dec 13, 2024 at 01:01:19PM -0300, Fabiano Rosas wrote: > 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 > Signed-off-by: Fabiano Rosas <farosas@suse.de> Reviewed-by: Peter Xu <peterx@redhat.com>
diff --git a/migration/multifd.c b/migration/multifd.c index 498e71fd10..8d0a763a72 100644 --- a/migration/multifd.c +++ b/migration/multifd.c @@ -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); @@ -1151,9 +1150,13 @@ 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 Signed-off-by: Fabiano Rosas <farosas@suse.de> --- migration/multifd.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)