rcu/srcutiny: don't return before reenabling preemption

Code after the return statement is dead. Enable preemption before
returning from srcu_drive_gp().

This will be important when/if PREEMPT_AUTO (lazy resched) gets merged.

Fixes: 65b4a59 ("srcu: Make Tiny SRCU explicitly disable preemption")
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Author: michich

kernel/rcu/srcutiny.c

@@ -122,8 +122,8 @@ void srcu_drive_gp(struct work_struct *wp)
 	ssp = container_of(wp, struct srcu_struct, srcu_work);
 	preempt_disable();  // Needed for PREEMPT_AUTO
 	if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) {
-		return; /* Already running or nothing to do. */
 		preempt_enable();
+		return; /* Already running or nothing to do. */
 	}
 
 	/* Remove recently arrived callbacks and wait for readers. */