Re: [PATCH v3 13/16] KVM: selftests: Verify vCPU migration during IRQ delivery

[Josh Hilke]

On Tue, May 26, 2026 at 7:23 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Tue, Apr 21, 2026, Josh Hilke wrote:
> > +static inline int gettid(void)
>
> gettid() already exists in at least some of my environments:

Should we just use syscall(__NR_gettid) to avoid any compatibility
issues? It's only used once in the test.

> > +void pin_task_to_random_cpu(pthread_t task, cpu_set_t *possible_cpus)
> > +{
> > +     int i = 0, nr_cpus = CPU_COUNT(possible_cpus);
> > +     int cpu, target_idx;
> > +
> > +     target_idx = kvm_random_u64(&kvm_rng) % nr_cpus;
> > +
> > +     for (cpu = 0; i < nr_cpus; cpu++) {
>
> Shouldn't this be bounded on "cpu < nr_cpus"?  If 'i' gets to nr_cpus, it means
> "i == target_idx" was never taken.  And at that point, the loop will hang
> indefinitely because cpu will likely be waaaay out of bounds of possible_cpus,
> i.e. the loop will always continue.
>
> > +             if (!CPU_ISSET(cpu, possible_cpus))
> > +                     continue;
> > +
> > +             if (i == target_idx) {
> > +                     pin_task_to_cpu(task, cpu);
> > +                     return;
> > +             }
> > +             i++;
> > +     }

Ahh, true. I think it actually needs to be bounded on "cpu <
CPU_SETSIZE" so that we iterate through all of the CPUs.

> This should TEST_FAIL().  Or maybe "break" on the match, and the assert that
> i == target_idx?

Will do