rcu: Handle outgoing CPUs on exit from idle loop

This commit informs RCU of an outgoing CPU just before that CPU invokes
arch_cpu_idle_dead() during its last pass through the idle loop (via a
new CPU_DYING_IDLE notifier value).  This change means that RCU need not
deal with outgoing CPUs passing through the scheduler after informing
RCU that they are no longer online.  Note that removing the CPU from
the rcu_node ->qsmaskinit bit masks is done at CPU_DYING_IDLE time,
and orphaning callbacks is still done at CPU_DEAD time, the reason being
that at CPU_DEAD time we have another CPU that can adopt them.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 4744ef915acd..d028721748d4 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -95,6 +95,8 @@ enum {
                                         * Called on the new cpu, just before
                                         * enabling interrupts. Must not sleep,
                                         * must not fail */
+#define CPU_DYING_IDLE          0x000B /* CPU (unsigned)v dying, reached
+                                        * idle loop. */
 #define CPU_BROKEN              0x000C /* CPU (unsigned)v did not die properly,
                                         * perhaps due to preemption. */