percpu: fix early calls for spinlock in pcpu_stats

From 2c06e795162cb306c9707ec51d3e1deadb37f573 Mon Sep 17 00:00:00 2001
From: Dennis Zhou <dennisz@fb.com>
Date: Wed, 21 Jun 2017 10:17:09 -0700

Commit 30a5b536 ("percpu: expose statistics about percpu memory via
debugfs") introduces percpu memory statistics. pcpu_stats_chunk_alloc
takes the spin lock and disables/enables irqs on creation of a chunk. Irqs
are not enabled when the first chunk is initialized and thus kernels are
failing to boot with kernel debugging enabled. Fixed by changing _irq to
_irqsave and _irqrestore.

Fixes: 30a5b536 ("percpu: expose statistics about percpu memory via debugfs")
Signed-off-by: Dennis Zhou <dennisz@fb.com>
Reported-by: Alexander Levin <alexander.levin@verizon.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

mm/percpu-internal.h

@@ -116,13 +116,14 @@ static inline void pcpu_stats_area_dealloc(struct pcpu_chunk *chunk)
  */
 static inline void pcpu_stats_chunk_alloc(void)
 {
-	spin_lock_irq(&pcpu_lock);
+	unsigned long flags;
+	spin_lock_irqsave(&pcpu_lock, flags);
 
 	pcpu_stats.nr_chunks++;
 	pcpu_stats.nr_max_chunks =
 		max(pcpu_stats.nr_max_chunks, pcpu_stats.nr_chunks);
 
-	spin_unlock_irq(&pcpu_lock);
+	spin_unlock_irqrestore(&pcpu_lock, flags);
 }
 
 /*
@@ -130,11 +131,12 @@ static inline void pcpu_stats_chunk_alloc(void)
  */
 static inline void pcpu_stats_chunk_dealloc(void)
 {
-	spin_lock_irq(&pcpu_lock);
+	unsigned long flags;
+	spin_lock_irqsave(&pcpu_lock, flags);
 
 	pcpu_stats.nr_chunks--;
 
-	spin_unlock_irq(&pcpu_lock);
+	spin_unlock_irqrestore(&pcpu_lock, flags);
 }
 
 #else