Merge tag 'rcu-urgent.2022.10.20a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU fix from Paul McKenney:
 "Fix a regression caused by commit bf95b2b ("rcu: Switch polled
  grace-period APIs to ->gp_seq_polled"), which could incorrectly leave
  interrupts enabled after an early-boot call to synchronize_rcu().

  Such synchronize_rcu() calls must acquire leaf rcu_node locks in order
  to properly interact with polled grace periods, but the code did not
  take into account the possibility of synchronize_rcu() being invoked
  from the portion of the boot sequence during which interrupts are
  disabled.

  This commit therefore switches the lock acquisition and release from
  irq to irqsave/irqrestore"

* tag 'rcu-urgent.2022.10.20a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  rcu: Keep synchronize_rcu() from enabling irqs in early boot

Author: torvalds

kernel/rcu/tree.c

@@ -1403,30 +1403,32 @@ static void rcu_poll_gp_seq_end(unsigned long *snap)
 // where caller does not hold the root rcu_node structure's lock.
 static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
 {
+	unsigned long flags;
 	struct rcu_node *rnp = rcu_get_root();
 
 	if (rcu_init_invoked()) {
 		lockdep_assert_irqs_enabled();
-		raw_spin_lock_irq_rcu_node(rnp);
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	}
 	rcu_poll_gp_seq_start(snap);
 	if (rcu_init_invoked())
-		raw_spin_unlock_irq_rcu_node(rnp);
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 }
 
 // Make the polled API aware of the end of a grace period, but where
 // caller does not hold the root rcu_node structure's lock.
 static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap)
 {
+	unsigned long flags;
 	struct rcu_node *rnp = rcu_get_root();
 
 	if (rcu_init_invoked()) {
 		lockdep_assert_irqs_enabled();
-		raw_spin_lock_irq_rcu_node(rnp);
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	}
 	rcu_poll_gp_seq_end(snap);
 	if (rcu_init_invoked())
-		raw_spin_unlock_irq_rcu_node(rnp);
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 }
 
 /*