Re: [Qemu-devel] [RFC PATCH v4 13/23] cpus: only take BQL for sleeping threads

["Pavel Dovgalyuk" <dovgaluk@ispras.ru>]

> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> On 19/01/2018 09:44, Pavel Dovgalyuk wrote:
> >      while (all_cpu_threads_idle()) {
> > +        qemu_mutex_lock_iothread();
> >          stop_tcg_kick_timer();
> >          qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
> > +        qemu_mutex_unlock_iothread();
> >      }
> 
> cpu_has_work cannot be called outside BQL yet.  You first need to access
> cpu->interrupt_request with atomics.
> 
> In general, testing the condition outside the mutex is a very dangerous
> pattern (and I'm usually the one who enjoys dangerous patterns).

It means, that I'll have to fix all the has_work function to avoid races,
because x86_cpu_has_work may have them?

static bool x86_cpu_has_work(CPUState *cs)
{
    X86CPU *cpu = X86_CPU(cs);
    CPUX86State *env = &cpu->env;

    return ((cs->interrupt_request & (CPU_INTERRUPT_HARD |
                                      CPU_INTERRUPT_POLL)) &&
            (env->eflags & IF_MASK)) ||
           (cs->interrupt_request & (CPU_INTERRUPT_NMI |
                                     CPU_INTERRUPT_INIT |
                                     CPU_INTERRUPT_SIPI |
                                     CPU_INTERRUPT_MCE)) ||
           ((cs->interrupt_request & CPU_INTERRUPT_SMI) &&
            !(env->hflags & HF_SMM_MASK));
}

Pavel Dovgalyuk