Hi,
On Thu, Mar 5, 2020 at 3:30 AM Maulik Shah <mkshah@xxxxxxxxxxxxxx> wrote:
>
> >> + spin_unlock_irqrestore(&ctrlr->cache_lock, flags);
> >> + return -EINVAL;
> > nit: why not add "int ret = 0" to the top of the function, then here:
> >
> > if (rpmh_flush(ctrl))
> > ret = -EINVAL;
> >
> > ...then at the end "return ret". It avoids the 2nd copy of the unlock?
> Done.
> >
> > Also: Why throw away the return value of rpmh_flush and replace it
> > with -EINVAL? Trying to avoid -EBUSY? ...oh, should you handle
> > -EBUSY? AKA:
> >
> > if (!psci_has_osi_support()) {
> > do {
> > ret = rpmh_flush(ctrl);
> > } while (ret == -EBUSY);
> > }
>
> Done, the return value from rpmh_flush() can be -EAGAIN, not -EBUSY.
>
> i will update the comment accordingly and will include below change as well in next series.
>
> https://patchwork.kernel.org/patch/11364067/
>
> this should address for caller to not handle -EAGAIN.
A few issues, I guess.
1. I _think_ it's important that you enable interrupts between
retries. If you're on the same CPU that the interrupt is routed to
and you were waiting for 'tcs_in_use' to be cleared you'll be in
trouble otherwise. ...I think we need to audit all of the places that
are looping based on -EAGAIN and confirm that interrupts are enabled
between retries. Before your patch series the only looping I see was
in rpmh_invalidate() and the lock wasn't held. After your series it's
also in rpmh_flush() which is called under spin_lock_irqsave() which
will be a problem.
2. The RPMH code uses both -EBUSY and -EAGAIN so I looked carefully at
this again. You're right that -EBUSY seems to be exclusively returned
by things only called by rpmh_rsc_send_data() and that function
handles the retries. ...but looking at this made me find a broken
corner case with the "zero active tcs" case (assuming you care about
this case as per your other thread). Specifically if you have "zero
active tcs" then get_tcs_for_msg() can call rpmh_rsc_invalidate()
which can return -EAGAIN. That will return the -EAGAIN out of
tcs_write() into rpmh_rsc_send_data(). rpmh_rsc_send_data() only
handles -EBUSY, not -EAGAIN.
-Doug
