hotplug: Prevent alloc/free of irq descriptors during cpu up/down (again)

Now that Xen no longer allocates irqs in _cpu_up() we can restore
commit a899418167 ("hotplug: Prevent alloc/free of irq descriptors
during cpu up/down")

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
CC: x86@kernel.org
CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

arch/x86/kernel/smpboot.c

@@ -1115,17 +1115,8 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 
 	common_cpu_up(cpu, tidle);
 
-	/*
-	 * We have to walk the irq descriptors to setup the vector
-	 * space for the cpu which comes online.  Prevent irq
-	 * alloc/free across the bringup.
-	 */
-	irq_lock_sparse();
-
 	err = do_boot_cpu(apicid, cpu, tidle);
-
 	if (err) {
-		irq_unlock_sparse();
 		pr_err("do_boot_cpu failed(%d) to wakeup CPU#%u\n", err, cpu);
 		return -EIO;
 	}
@@ -1143,8 +1134,6 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 		touch_nmi_watchdog();
 	}
 
-	irq_unlock_sparse();
-
 	return 0;
 }
 

kernel/cpu.c

@@ -349,8 +349,16 @@ static int bringup_cpu(unsigned int cpu)
 	struct task_struct *idle = idle_thread_get(cpu);
 	int ret;
 
+	/*
+	 * Some architectures have to walk the irq descriptors to
+	 * setup the vector space for the cpu which comes online.
+	 * Prevent irq alloc/free across the bringup.
+	 */
+	irq_lock_sparse();
+
 	/* Arch-specific enabling code. */
 	ret = __cpu_up(cpu, idle);
+	irq_unlock_sparse();
 	if (ret) {
 		cpu_notify(CPU_UP_CANCELED, cpu);
 		return ret;