On Fri, May 29, 2020 at 04:41:32PM +1000, Stephen Rothwell wrote:
> Hi all,
>
> On Fri, 29 May 2020 16:22:34 +1000 Stephen Rothwell <s...@canb.auug.org.au>
> wrote:
> >
> > Hi all,
> >
> > Today's linux-next merge of the rcu tree got a conflict in:
> >
> > kernel/rcu/tree.c
> >
> > between commits:
> >
> > 806f04e9fd2c ("rcu: Allow for smp_call_function() running callbacks from
> > idle")
> > aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from
> > rcu_nmi_enter()")
> >
> > from the tip tree and commit:
> >
> > c0601bb42994 ("rcu/tree: Clean up dynticks counter usage")
> > 3f3baaf3ac07 ("rcu/tree: Remove dynticks_nmi_nesting counter")
> >
> > from the rcu tree.
> >
> > I fixed it up (I punted and took some from the former and some from the
> > latter) and can carry the fix as necessary. This is now fixed as far as
> > linux-next is concerned, but any non trivial conflicts should be mentioned
> > to your upstream maintainer when your tree is submitted for merging.
> > You may also want to consider cooperating with the maintainer of the
> > conflicting tree to minimise any particularly complex conflicts.
>
> I redid this and the resolution is below, but you should look at the
> final file when I do the release.
Given that the merge window might be opening in a couple days, my thought
is to defer these -rcu commits to my v5.9 pile, and then I resolve this
conflict in the -rcu tree when v5.8-rc1 comes out. I just now adjusted
the -rcu tree's rcu/next branch accordingly.
Seem reasonable?
Thanx, Paul
> --
> Cheers,
> Stephen Rothwell
>
> diff --cc kernel/rcu/tree.c
> index c716eadc7617,78125749638f..1426b968eec1
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@@ -427,14 -385,8 +386,12 @@@ EXPORT_SYMBOL_GPL(rcu_momentary_dyntick
> */
> static int rcu_is_cpu_rrupt_from_idle(void)
> {
> - long nesting;
> -
> - /* Called only from within the scheduling-clock interrupt */
> - lockdep_assert_in_irq();
> + /*
> + * Usually called from the tick; but also used from smp_function_call()
> + * for expedited grace periods. This latter can result in running from
> + * the idle task, instead of an actual IPI.
> + */
> + lockdep_assert_irqs_disabled();
>
> /* Check for counter underflows */
> RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0,
> @@@ -778,24 -718,6 +723,21 @@@ void rcu_irq_exit_preempt(void
> "RCU in extended quiescent state!");
> }
>
> +#ifdef CONFIG_PROVE_RCU
> +/**
> + * rcu_irq_exit_check_preempt - Validate that scheduling is possible
> + */
> +void rcu_irq_exit_check_preempt(void)
> +{
> + lockdep_assert_irqs_disabled();
> +
> + RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) <= 0,
> + "RCU dynticks_nesting counter underflow/zero!");
> - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) !=
> - DYNTICK_IRQ_NONIDLE,
> - "Bad RCU dynticks_nmi_nesting counter\n");
> + RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
> + "RCU in extended quiescent state!");
> +}
> +#endif /* #ifdef CONFIG_PROVE_RCU */
> +
> /*
> * Wrapper for rcu_irq_exit() where interrupts are enabled.
> *
