linux-kernel - [PATCH 1/1] percpu: fix early calls for spinlock in pcpu

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Message-ID: <20170621175245.GA99514@dennisz-mbp.dhcp.thefacebook.com>
Date:   Wed, 21 Jun 2017 13:52:46 -0400
From:   Dennis Zhou <dennisz@...com>
To:     "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>,
        Tejun Heo <tj@...nel.org>
CC:     Christoph Lameter <cl@...ux.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-team@...com" <kernel-team@...com>
Subject: [PATCH 1/1] percpu: fix early calls for spinlock in pcpu_stats

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

Commit 30a5b5367ef9 ("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: 30a5b5367ef9 ("percpu: expose statistics about percpu memory via debugfs")
Signed-off-by: Dennis Zhou <dennisz@...com>
Reported-by: Alexander Levin <alexander.levin@...izon.com>
---

Hi Sasha,

The root cause was from 0003 of that series where I prematurely enabled
irqs and the problem is addresssed here. I am able to boot with debug
options enabled.

Thanks,
Dennis

 mm/percpu-internal.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h
index d030fce..cd2442e 100644
--- a/mm/percpu-internal.h
+++ b/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
-- 
2.9.3