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On Fri, Nov 11, 2022 at 02:54:38PM +0530, Shaleen Bathla wrote:
> Problem:
> libvirt has a 5 second timeout (generally) for hotplug/unplug
> operations which can time out due to heavy load in guest.
>
> vcpu hotunplug occurs one vcpu at a time.
> But, if we perform hotplug-unplug repeatedly,
> Case 1: qemu sends multiple timedout vcpu unplug notification before
> libvirt processed first one.
> Case 2: when attempting a hotplug, qemu finishes unplug of another cpu
>
> libvirt waits for an async event notification from qemu regarding
> successful vcpu delete.
> qemu deletes its vcpu, vcpuinfo and sends notification to libvirt.
> libvirt handles vcpu delete notification, and updates vcpuinfo
> received from qemu in qemuDomainRefreshVcpuInfo().
>
> qemu's vcpuinfo during refresh will not contain other deleted, sent vcpu
> qemu's vcpuinfo will overwrite libvirt's vcpuinfo of the other pending
> timedout vcpu(s) which qemu has deleted and notified libvirt.
> The overwrite resets other timedout vcpu's alias to NULL and tid to 0.
>
> The error is then seen when validating tid of vcpus.
> Example error log:
> "internal error: qemu didn't report thread id for vcpu 'XX'"
>
> Solution:
> Clear vcpu alias of only the vcpu that hotplug API calls.
> Other vcpu-alias won't get reset when vcpuinfo refresh occurs.
> Validation is also done for corresponding vcpus only, not all.
>
> Co-authored-by: Partha Satapathy <partha.satapathy@xxxxxxxxxx>
> Signed-off-by: Shaleen Bathla <shaleen.bathla@xxxxxxxxxx>
> ---
> src/qemu/qemu_domain.c | 6 ++++--
> src/qemu/qemu_hotplug.c | 39 +++++++++++++++++++++++++++++++--------
> 2 files changed, 35 insertions(+), 10 deletions(-)
>
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 3435da5bdc4c..6ae842d0e32f 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -9773,8 +9773,10 @@ qemuDomainRefreshVcpuInfo(virDomainObj *vm,
> vcpupriv->vcpus = info[i].vcpus;
> VIR_FREE(vcpupriv->type);
> vcpupriv->type = g_steal_pointer(&info[i].type);
> - VIR_FREE(vcpupriv->alias);
> - vcpupriv->alias = g_steal_pointer(&info[i].alias);
> + if (info[i].alias) {
> + VIR_FREE(vcpupriv->alias);
> + vcpupriv->alias = g_steal_pointer(&info[i].alias);
> + }
> virJSONValueFree(vcpupriv->props);
> vcpupriv->props = g_steal_pointer(&info[i].props);
> vcpupriv->enable_id = info[i].id;
> diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
> index da92ced2f444..f11b90a220ac 100644
> --- a/src/qemu/qemu_hotplug.c
> +++ b/src/qemu/qemu_hotplug.c
> @@ -6090,6 +6090,8 @@ qemuDomainRemoveVcpu(virDomainObj *vm,
> unsigned int nvcpus = vcpupriv->vcpus;
> virErrorPtr save_error = NULL;
> size_t i;
> + bool hasVcpuPids = qemuDomainHasVcpuPids(vm);
> + bool rollback = false;
>
> if (qemuDomainRefreshVcpuInfo(vm, VIR_ASYNC_JOB_NONE, false) < 0)
> return -1;
> @@ -6097,14 +6099,26 @@ qemuDomainRemoveVcpu(virDomainObj *vm,
> /* validation requires us to set the expected state prior to calling it */
> for (i = vcpu; i < vcpu + nvcpus; i++) {
> vcpuinfo = virDomainDefGetVcpu(vm->def, i);
> + vcpupriv = QEMU_DOMAIN_VCPU_PRIVATE(vcpuinfo);
> +
> vcpuinfo->online = false;
> + VIR_FREE(vcpupriv->alias); /* clear vcpu alias of only this vcpu */
> +
> + if (vcpupriv->tid != 0) {
> + if (hasVcpuPids)
> + virReportError(VIR_ERR_INTERNAL_ERROR,
> + _("qemu reported thread id for inactive vcpu '%zu'"), i);
> +
> + rollback = true;
> + break;
> + }
> }
>
> - if (qemuDomainValidateVcpuInfo(vm) < 0) {
> + if (rollback) {
> /* rollback vcpu count if the setting has failed */
> virDomainAuditVcpu(vm, oldvcpus, oldvcpus - nvcpus, "update", false);
>
> - for (i = vcpu; i < vcpu + nvcpus; i++) {
> + for (; i >= vcpu; i--) {
> vcpuinfo = virDomainDefGetVcpu(vm->def, i);
> vcpuinfo->online = true;
> }
> @@ -6141,6 +6155,9 @@ qemuDomainRemoveVcpuAlias(virDomainObj *vm,
> return;
> }
> }
> +
> + VIR_DEBUG("%s not found in vcpulist of domain %s ",
> + alias, vm->def->name);
> }
>
>
> @@ -6209,6 +6226,7 @@ qemuDomainHotplugAddVcpu(virQEMUDriver *driver,
> int rc;
> int oldvcpus = virDomainDefGetVcpus(vm->def);
> size_t i;
> + bool hasVcpuPids = qemuDomainHasVcpuPids(vm);
>
> if (!qemuDomainSupportsNewVcpuHotplug(vm)) {
> virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
> @@ -6245,14 +6263,19 @@ qemuDomainHotplugAddVcpu(virQEMUDriver *driver,
>
> vcpuinfo->online = true;
>
> - if (vcpupriv->tid > 0 &&
> - qemuProcessSetupVcpu(vm, i, true) < 0)
> - return -1;
> + if (vcpupriv->tid > 0) {
> + if (qemuProcessSetupVcpu(vm, i, true) < 0) {
> + return -1;
> + }
> + } else {
> + if (hasVcpuPids) {
> + virReportError(VIR_ERR_INTERNAL_ERROR,
> + _("qemu didn't report thread id for vcpu '%zu'"), i);
> + return -1;
> + }
> + }
> }
>
> - if (qemuDomainValidateVcpuInfo(vm) < 0)
> - return -1;
> -
> qemuDomainVcpuPersistOrder(vm->def);
>
> if (virDomainObjSave(vm, driver->xmlopt, cfg->stateDir) < 0)
> --
> 2.31.1
>
> V1 Patch :
> https://listman.redhat.com/archives/libvir-list/2022-November/235470.html
>
> V1 Patch Review comments :
> https://listman.redhat.com/archives/libvir-list/2022-November/235534.html
>
> Changes in V2 since V1:
> - Patch addresses review comments from Peter Krempa.
> - Validation is done for per cpu hotplug entity instead of all
