On Wed, Feb 12, 2025 at 13:33:46 +0100, Peter Krempa wrote:
On incoming migration qemu doesn't activate the block graph nodes right away. This is to properly facilitate locking of the images.
The block nodes are normally re-activated when starting the CPUs after migration, but in cases (e.g. when a paused VM was migrated) when the VM is left paused the block nodes are not re-activated by qemu.
This means that blockjobs which would want to write to an existing backing chain member would fail. Generally read-only jobs would succeed with older qemu's but this was not intended.
Instead with new qemu you'll always get an error if attempting to access a inactive node:
error: internal error: unable to execute QEMU command 'blockdev-mirror': Inactive 'libvirt-1-storage' can't be a backing child of active '#block052'
This is the case for explicit blockjobs (virsh blockcopy) but also for non shared-storage migration (virsh migrate --copy-storage-all).
Since qemu now provides 'blockdev-set-active' QMP command which can on-demand re-activate the nodes we can re-activate them in similar cases as when we'd be starting vCPUs if the VM weren't left paused.
The only exception is on the source in case of a failed post-copy migration as the VM already ran on destination so it won't ever run on the source even when recovered.
Resolves: https://issues.redhat.com/browse/RHEL-78398 Signed-off-by: Peter Krempa <pkrempa@redhat.com> ---
v2: - qemuMigrationBlockNodesReactivate now preserves previous errors - qemuMigrationSrcRestoreDomainState: - separated post-copy failure state to avoid reactivation - moved the reactivation under a label - reactivating also when resuming of cpus fails
src/qemu/qemu_migration.c | 56 ++++++++++++++++++++++++++++++++++++--- 1 file changed, 52 insertions(+), 4 deletions(-)
diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c index 53bbbee629..b36d779657 100644 --- a/src/qemu/qemu_migration.c +++ b/src/qemu/qemu_migration.c @@ -220,6 +220,43 @@ qemuMigrationSrcStoreDomainState(virDomainObj *vm) }
+/** + * qemuMigrationBlockNodesReactivate: + * + * In case when we're keeping the VM paused qemu will not re-activate the block + * device backend tree so blockjobs would fail. In case when qemu supports the + * 'blockdev-set-active' command this function will re-activate the block nodes. + */ +static void +qemuMigrationBlockNodesReactivate(virDomainObj *vm, + virDomainAsyncJob asyncJob) +{ + virErrorPtr orig_err; + qemuDomainObjPrivate *priv = vm->privateData; + int rc; + + if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV_SET_ACTIVE)) + return; + + VIR_DEBUG("re-activating block nodes"); + + virErrorPreserveLast(&orig_err); + + if (qemuDomainObjEnterMonitorAsync(vm, asyncJob) < 0) + goto cleanup; + + rc = qemuMonitorBlockdevSetActive(priv->mon, NULL, true); + + qemuDomainObjExitMonitor(vm); + + if (rc < 0) + VIR_WARN("failed to re-activate block nodes after migration of VM '%s'", vm->def->name); + + cleanup: + virErrorRestore(&orig_err); +} + + static void qemuMigrationSrcRestoreDomainState(virQEMUDriver *driver, virDomainObj *vm) { @@ -236,14 +273,16 @@ qemuMigrationSrcRestoreDomainState(virQEMUDriver *driver, virDomainObj *vm) virDomainStateTypeToString(state), virDomainStateReasonToString(state, reason));
- if (preMigrationState != VIR_DOMAIN_RUNNING || - state != VIR_DOMAIN_PAUSED || - reason == VIR_DOMAIN_PAUSED_POSTCOPY_FAILED) + if (reason == VIR_DOMAIN_PAUSED_POSTCOPY_FAILED)
state == VIR_DOMAIN_PAUSED && reason == VIR_DOMAIN_PAUSED_POSTCOPY_FAILED otherwise you could be comparing completely unrelated numbers
return;
+ if (preMigrationState != VIR_DOMAIN_RUNNING || + state != VIR_DOMAIN_PAUSED) + goto reactivate; + if (reason == VIR_DOMAIN_PAUSED_IOERROR) { VIR_DEBUG("Domain is paused due to I/O error, skipping resume"); - return; + goto reactivate; }
VIR_DEBUG("Restoring pre-migration state due to migration error");
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>