Re: [PATCH] Fix QEMU vcpu thread race with apic_reset

[Ulrich Drepper <drepper@redhat.com>]

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Ryan Harper wrote:
> @@ -388,9 +395,10 @@ static void kvm_add_signal(struct qemu_kvm_signal_table *sigtab, int signum)
>  
>  void kvm_init_new_ap(int cpu, CPUState *env)
>  {
> +    pthread_mutex_lock(&vcpu_mutex);
>      pthread_create(&vcpu_info[cpu].thread, NULL, ap_main_loop, env);
> -    /* FIXME: wait for thread to spin up */
> -    usleep(200);
> +    pthread_cond_wait(&qemu_vcpuup_cond, &vcpu_mutex);
> +    pthread_mutex_unlock(&vcpu_mutex);

And something is very wrong here.  The pattern for using a condvar is

1 take mutex

2 check condition

3 if condition is not fulfilled
3a   call cond_wait
3b   when returning, go back to step 2

4 unlock mutex


Anything else is buggy.

So, either your condvar use is wrong or you don't really want a condvar
in the first place.  I haven't checked the code.

- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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