Date: Wed, 21 Jun 2017 13:52:46 -0400
From: Dennis Zhou <dennisz@fb.com>
To: "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com>,
        Tejun Heo <tj@kernel.org>
CC: Christoph Lameter <cl@linux.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kernel-team@fb.com" <kernel-team@fb.com>
Subject: [PATCH 1/1] percpu: fix early calls for spinlock in pcpu_stats
Message-ID: <20170621175245.GA99514@dennisz-mbp.dhcp.thefacebook.com>
References: <20170619232832.27116-1-dennisz@fb.com>
 <20170619232832.27116-5-dennisz@fb.com>
 <20170621161836.tv67op4hokja35bc@sasha-lappy>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20170621161836.tv67op4hokja35bc@sasha-lappy>
User-Agent: Mutt/1.6.1 (2016-04-27)
SpamDiagnosticOutput: 1:99
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Jun 2017 17:52:53.4183 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN1PR15MB0510
X-OriginatorOrg: fb.com
X-Proofpoint-Spam-Reason: safe
X-FB-Internal: Safe
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-06-21_04:,,
 signatures=0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1931
Lines: 66

>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 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@fb.com>
Reported-by: Alexander Levin <alexander.levin@verizon.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