[PATCH 4.2.y-ckt 158/305] of/fdt: Add mutex protection for calls to __unflatten_device_tree()

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Guenter Roeck <linux@roeck-us.net>

commit f8062386671a596ca7022c61727a14a25679a0a1 upstream.

__unflatten_device_tree() calls unflatten_dt_node(), which declares
a static variable. It is therefore not reentrant.

One of the callers of __unflatten_device_tree(), unflatten_device_tree(),
is only called once during early initialization and does not need to be
protected. The other caller, of_fdt_unflatten_tree(), can be called at
any time, possibly multiple times in parallel. This can happen, for
example, if multiple devicetree overlays have to be loaded and installed.

Without this protection, errors such as the following may be seen.

kernel: End of tree marker overwritten: e6a3a458
kernel: find_target_node:
	Failed to find target-indirect node at /fragment@0
kernel: __of_overlay_create: of_build_overlay_info() failed for tree@/

Add a mutex to of_fdt_unflatten_tree() to make the call reentrant.

Cc: Pantelis Antoniou <redacted>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kamal Mostafa <redacted>
---
 drivers/of/fdt.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index d1bfd89..049caf7 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c

@@ -13,6 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/initrd.h>
 #include <linux/memblock.h>
+#include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/of_fdt.h>
 #include <linux/of_reserved_mem.h>

@@ -436,6 +437,8 @@ static void *kernel_tree_alloc(u64 size, u64 align)
 	return kzalloc(size, GFP_KERNEL);
 }
 
+static DEFINE_MUTEX(of_fdt_unflatten_mutex);
+
 /**
  * of_fdt_unflatten_tree - create tree of device_nodes from flat blob
  *

@@ -447,7 +450,9 @@ static void *kernel_tree_alloc(u64 size, u64 align)
 void of_fdt_unflatten_tree(const unsigned long *blob,
 			struct device_node **mynodes)
 {
+	mutex_lock(&of_fdt_unflatten_mutex);
 	__unflatten_device_tree(blob, mynodes, &kernel_tree_alloc);
+	mutex_unlock(&of_fdt_unflatten_mutex);
 }
 EXPORT_SYMBOL_GPL(of_fdt_unflatten_tree);
 

-- 
1.9.1