linux-kernel - [PATCH 2/3] memory_hotplug: add note about holding device_hotplug_lock and add

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Message-Id: <1423669462-30918-3-git-send-email-vkuznets@redhat.com>
Date:	Wed, 11 Feb 2015 16:44:21 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	Fabian Frederick <fabf@...net.be>,
	Zhang Zhen <zhenzhang.zhang@...wei.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Wang Nan <wangnan0@...wei.com>
Cc:	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	linux-mm@...ck.org
Subject: [PATCH 2/3] memory_hotplug: add note about holding device_hotplug_lock and add_memory()

add_memory() is supposed to be run with device_hotplug_lock grabbed, otherwise
it can race with e.g. device_online(). ACPI memory hotplug does that already
but e.g. Hyper-V ballooning driver doesn't.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 mm/memory_hotplug.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 9fab107..41638eb 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1213,7 +1213,11 @@ int zone_for_memory(int nid, u64 start, u64 size, int zone_default)
 	return zone_default;
 }
 
-/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
+/*
+ * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
+ * and online/offline operations before this call.
+ * We are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG.
+ */
 int __ref add_memory(int nid, u64 start, u64 size)
 {
 	pg_data_t *pgdat = NULL;
-- 
1.9.3

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