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SubjectRe: linux-next: manual merge of the rcu tree with the tip tree
Hi all,

On Fri, 29 May 2020 16:22:34 +1000 Stephen Rothwell <sfr@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.

--
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.
*
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