Re: [Qemu-devel] Re: [PATCH 08/10] MCE: Relay UCR MCE to guest

Marcelo Tosatti
2010-10-20T21:40:07Z

On Wed, Oct 20, 2010 at 03:59:29PM -0500, Anthony Liguori wrote:
> On 10/20/2010 02:51 PM, Anthony Liguori wrote:
> >
> >>+}
> >>+
> >> static void qemu_kvm_eat_signal(CPUState *env, int timeout)
> >> {
> >> struct timespec ts;
> >> int r, e;
> >> siginfo_t siginfo;
> >> sigset_t waitset;
> >>+ sigset_t chkset;
> >>
> >> ts.tv_sec = timeout / 1000;
> >> ts.tv_nsec = (timeout % 1000) * 1000000;
> >>
> >> sigemptyset(&waitset);
> >> sigaddset(&waitset, SIG_IPI);
> >>+ sigaddset(&waitset, SIGBUS);
> >>
> >>- qemu_mutex_unlock(&qemu_global_mutex);
> >>- r = sigtimedwait(&waitset,&siginfo,&ts);
> >>- e = errno;
> >>- qemu_mutex_lock(&qemu_global_mutex);
> >>+ do {
> >>+ qemu_mutex_unlock(&qemu_global_mutex);
> >>
> >>- if (r == -1&& !(e == EAGAIN || e == EINTR)) {
> >>- fprintf(stderr, "sigtimedwait: %s\n", strerror(e));
> >>- exit(1);
> >>- }
> >>+ r = sigtimedwait(&waitset,&siginfo,&ts);
> >>+ e = errno;
> >>+
> >>+ qemu_mutex_lock(&qemu_global_mutex);
> >>+
> >>+ if (r == -1&& !(e == EAGAIN || e == EINTR)) {
> >>+ fprintf(stderr, "sigtimedwait: %s\n", strerror(e));
> >>+ exit(1);
> >>+ }
> >>+
> >>+ switch (r) {
> >>+ case SIGBUS:
> >>+#ifdef TARGET_I386
> >>+ if (kvm_on_sigbus_vcpu(env, siginfo.si_code,
> >>siginfo.si_addr))
> >>+#endif
> >>+ sigbus_reraise();
> >>+ break;
> >>+ default:
> >>+ break;
> >>+ }
> >>+
> >>+ r = sigpending(&chkset);
> >>+ if (r == -1) {
> >>+ fprintf(stderr, "sigpending: %s\n", strerror(e));
> >>+ exit(1);
> >>+ }
> >>+ } while (sigismember(&chkset, SIG_IPI) ||
> >>sigismember(&chkset, SIGBUS));
> >> }
> >
> >I don't understand why this loop is needed but we specifically
> >wait for a signal to get delivered that's either SIG_IPI or
> >SIGBUS. We then check whether a SIG_IPI or SIGBUS is pending and
> >loop waiting for signals again.
> >
> >Shouldn't we be looping on just sigismember(SIGBUS)?
> >
> >BTW, we're no longer respecting timeout because we're not
> >adjusting ts after each iteration.
>
> I think this is important too. The last time I went through the
> code and played around here, it wasn't possible to set timeout to a
> very, very large value because there are still things that we poll
> for (like whether shutdown has occurred). If we loop indefinitely
> without reducing ts, we can potentially recreate an infinite timeout
> which means we won't catch any of the events we poll for. This
> would be a very, very subtle bug to track down.

We should just kill timeout parameter, i don't see any use for it.