On Wed, May 20, 2020 at 09:24:46PM +0200, Thomas Gleixner wrote:
> Andy Lutomirski <[email protected]> writes:
> > On Wed, May 20, 2020 at 8:36 AM Andy Lutomirski <[email protected]> wrote:
> > if (user_mode(regs)) {
> > enter_from_user_mode();
> > } else {
> > if (!__rcu_is_watching()) {
> > /*
> > * If RCU is not watching then the same careful
> > * sequence vs. lockdep and tracing is required.
> > *
> > * This only happens for IRQs that hit the idle loop, and
> > * even that only happens if we aren't using the sane
> > * MWAIT-while-IF=0 mode.
> > */
> > lockdep_hardirqs_off(CALLER_ADDR0);
> > rcu_irq_enter();
> > instrumentation_begin();
> > trace_hardirqs_off_prepare();
> > instrumentation_end();
> > return true;
> > } else {
> > /*
> > * If RCU is watching then the combo function
> > * can be used.
> > */
> > instrumentation_begin();
> > trace_hardirqs_off();
> > rcu_tickle();
> > instrumentation_end();
> > }
> > }
> > return false;
> >
> > This is exactly what you have except that the cond_rcu part is gone
> > and I added rcu_tickle().
> >
> > Paul, the major change here is that if an IRQ hits normal kernel code
> > (i.e. code where RCU is watching and we're not in an EQS), the IRQ
> > won't call rcu_irq_enter() and rcu_irq_exit(). Instead it will call
> > rcu_tickle() on entry and nothing on exit. Does that cover all the
> > bases?
>
> Just chatted with Paul on IRC and he thinks this should work, but he's
> not sure whether it's actually sane :)
I will have more to say after coding it up. ;-)
Thanx, Paul
