Messages in this thread | | | Date | Sun, 10 Jun 2012 22:29:17 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH] rcu: Allow calls to rcu_exit_user_irq from nesting irqs |
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On Sun, Jun 10, 2012 at 11:06:59AM -0700, Paul E. McKenney wrote: > On Sun, Jun 10, 2012 at 12:55:54AM +0200, Frederic Weisbecker wrote: > > void rcu_user_enter_irq(void) > > { > > @@ -478,12 +478,9 @@ void rcu_user_enter_irq(void) > > > > local_irq_save(flags); > > rdtp = &__get_cpu_var(rcu_dynticks); > > - /* > > - * Ensure this irq is a non nesting one interrupting > > - * a non-idle RCU state. > > - */ > > - WARN_ON_ONCE(rdtp->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE + 1); > > - rdtp->dynticks_nesting = 1; > > + /* Ensure we are interrupting a non-idle RCU state */ > > + WARN_ON_ONCE(!(rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK)); > > + rdtp->dynticks_nesting -= DYNTICK_TASK_EXIT_IDLE; > > This will be broken on architectures that can fail to return from interrupts > and exceptions and vice versa. The resulting value of rdtp->dynticks_nesting > might well go negative, or might fail to reach zero when the outermost > interrupt returns. > > One workaround would be to add up the relevant fields of preempt_count() > and assign the result to rdtp->dynticks_nesting.
That's ok. I made rcu_user_enter_irq() to support nesting irqs in order to stay consistant with the same change in rcu_user_exit_irq(). But this is not necessary. rcu_user_enter_irq() itself is only called from the outermost irq.
Also there is a sanity check that ensures that in the current code in rcu/idle tree so rcu_user_enter_irq() can stay as is there.
I'll resend the patch with only the change in rcu_user_exit_irq().
Thanks.
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