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Date:   Sun, 12 Feb 2017 14:34:22 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     akpm@...ux-foundation.org
Cc:     Michal Hocko <mhocko@...e.com>, Toshi Kani <toshi.kani@....com>,
        Ben Hutchings <ben@...adent.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org,
        Logan Gunthorpe <logang@...tatee.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 2/2] mm: validate device_hotplug is held for memory hotplug

mem_hotplug_begin() assumes that it can set mem_hotplug.active_writer
and run the hotplug process without racing another thread. Validate this
assumption with a lockdep assertion.

Cc: Michal Hocko <mhocko@...e.com>
Cc: Toshi Kani <toshi.kani@....com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Logan Gunthorpe <logang@...tatee.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Reported-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/base/core.c    |    5 +++++
 include/linux/device.h |    1 +
 mm/memory_hotplug.c    |    2 ++
 3 files changed, 8 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 8c25e68e67d7..3050e6f99403 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -638,6 +638,11 @@ int lock_device_hotplug_sysfs(void)
 	return restart_syscall();
 }
 
+void assert_held_device_hotplug(void)
+{
+	lockdep_assert_held(&device_hotplug_lock);
+}
+
 #ifdef CONFIG_BLOCK
 static inline int device_is_not_partition(struct device *dev)
 {
diff --git a/include/linux/device.h b/include/linux/device.h
index bd684fc8ec1d..a48a7ff70164 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1139,6 +1139,7 @@ static inline bool device_supports_offline(struct device *dev)
 extern void lock_device_hotplug(void);
 extern void unlock_device_hotplug(void);
 extern int lock_device_hotplug_sysfs(void);
+void assert_held_device_hotplug(void);
 extern int device_offline(struct device *dev);
 extern int device_online(struct device *dev);
 extern void set_primary_fwnode(struct device *dev, struct fwnode_handle *fwnode);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 19b460acb5e1..0ab3dd6cc2a4 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -126,6 +126,8 @@ void put_online_mems(void)
 
 void mem_hotplug_begin(void)
 {
+	assert_held_device_hotplug();
+
 	mem_hotplug.active_writer = current;
 
 	memhp_lock_acquire();

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