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From:   Shile Zhang <shile.zhang@linux.alibaba.com>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@oracle.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Shile Zhang <shile.zhang@linux.alibaba.com>
Subject: [PATCH 1/1] mm: fix tick_sched timer blocked by pgdat_resize_lock
Date:   Fri, 10 Jan 2020 16:25:10 +0800
Message-Id: <20200110082510.172517-2-shile.zhang@linux.alibaba.com>
In-Reply-To: <20200110082510.172517-1-shile.zhang@linux.alibaba.com>
References: <20200110082510.172517-1-shile.zhang@linux.alibaba.com>
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When 'CONFIG_DEFERRED_STRUCT_PAGE_INIT' is set, 'pgdat_resize_lock'
will be called inside 'pgdatinit' kthread to initialise the deferred
pages with local interrupts disabled. Which is introduced by
commit 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred
pages").

But 'pgdatinit' kthread is possible be pined on the boot CPU (CPU#0 by
default), especially in small system with NRCPUS <= 2. In this case, the
interrupts are disabled on boot CPU during memory initialising, which
caused the tick_sched timer be blocked, leading to wall clock stuck.

Fixes: commit 3a2d7fa8a3d5 ("mm: disable interrupts while initializing
deferred pages")

Signed-off-by: Shile Zhang <shile.zhang@linux.alibaba.com>
---
 include/linux/memory_hotplug.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index ba0dca6aac6e..6ffcb5b704bc 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -282,12 +282,22 @@ static inline bool movable_node_is_enabled(void)
 static inline
 void pgdat_resize_lock(struct pglist_data *pgdat, unsigned long *flags)
 {
-	spin_lock_irqsave(&pgdat->node_size_lock, *flags);
+	/*
+	 * Disable local interrupts on boot CPU will stop the tick_sched
+	 * timer, which will block jiffies(wall clock) update.
+	 */
+	if (current->cpu != get_boot_cpu_id())
+		spin_lock_irqsave(&pgdat->node_size_lock, *flags);
+	else
+		spin_lock(&pgdat->node_size_lock);
 }
 static inline
 void pgdat_resize_unlock(struct pglist_data *pgdat, unsigned long *flags)
 {
-	spin_unlock_irqrestore(&pgdat->node_size_lock, *flags);
+	if (current->cpu != get_boot_cpu_id())
+		spin_unlock_irqrestore(&pgdat->node_size_lock, *flags);
+	else
+		spin_unlock(&pgdat->node_size_lock);
 }
 static inline
 void pgdat_resize_init(struct pglist_data *pgdat)
-- 
2.24.0.rc2