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SubjectRe: [PATCH 1/2] xen/x86: Move irq allocation from Xen smp_op.cpu_up()
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On 03/25/2016 11:10 AM, Konrad Rzeszutek Wilk wrote:
> On Thu, Mar 17, 2016 at 09:33:32AM -0400, Boris Ostrovsky wrote:
>> Commit ce0d3c0a6fb1 ("genirq: Revert sparse irq locking around
>> __cpu_up() and move it to x86 for now") reverted irq locking
>> introduced by commit a89941816726 ("hotplug: Prevent alloc/free
>> of irq descriptors during cpu up/down") because of Xen allocating
>> irqs in both of its cpu_up ops.
>>
>> We can move those allocations into CPU notifiers so that original
>> patch can be reinstated.
> Original being "hotplug: Prevent alloc/free..." ?

Yes.

>
> -static int xen_hvm_cpu_notify(struct notifier_block *self, unsigned long action,
> - void *hcpu)
> +static int xen_cpu_notify(struct notifier_block *self, unsigned long action,
> + void *hcpu)
> {
> int cpu = (long)hcpu;
> + int rc;
> +
> switch (action) {
> case CPU_UP_PREPARE:
> - xen_vcpu_setup(cpu);
> - if (xen_have_vector_callback) {
> - if (xen_feature(XENFEAT_hvm_safe_pvclock))
> - xen_setup_timer(cpu);
> + if (xen_hvm_domain()) {
> + /*
> + * This can happen if CPU was offlined earlier and
> + * offlining timed out in common_cpu_die().
> + */
> + if (cpu_report_state(cpu) == CPU_DEAD_FROZEN) {
> + xen_smp_intr_free(cpu);
> + xen_uninit_lock_cpu(cpu);
> + }
> +
> + xen_vcpu_setup(cpu);
> }
> +
> + if (xen_pv_domain() ||
> + (xen_have_vector_callback &&
> + xen_feature(XENFEAT_hvm_safe_pvclock)))
> + xen_setup_timer(cpu);
> +
> + rc = xen_smp_intr_init(cpu);
> + if (rc) {
> + WARN(1, "xen_smp_intr_init() for CPU %d failed: %d\n",
> + cpu, rc);
> + return NOTIFY_BAD;
> + }
> +
> + break;
> + case CPU_ONLINE:
> + xen_init_lock_cpu(cpu);
> + break;
> + case CPU_UP_CANCELED:
> + xen_smp_intr_free(cpu);
> xen_uninit_lock_cpu ?

I don't think this is needed: we initialize lock in CPU_ONLINE notifier
which can only be called after CPU_UP_CANCELED would have run (in which
case we'll never do CPU_ONLINE)

-boris

>
>
>> + if (xen_pv_domain() ||
>> + (xen_have_vector_callback &&
>> + xen_feature(XENFEAT_hvm_safe_pvclock)))
>> + xen_teardown_timer(cpu);
>> break;
>> default:
>> break;

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