[4.2.y-ckt stable] Patch "of/fdt: Add mutex protection for calls to __unflatten_device_tree()" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    of/fdt: Add mutex protection for calls to __unflatten_device_tree()

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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

>From d37192683f95ad82438328b0aa89cc5793c19d26 Mon Sep 17 00:00:00 2001
From: Guenter Roeck <linux at roeck-us.net>
Date: Sat, 5 Dec 2015 16:13:53 -0800
Subject: of/fdt: Add mutex protection for calls to __unflatten_device_tree()

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 at 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 <pantelis.antoniou at konsulko.com>
Signed-off-by: Guenter Roeck <linux at roeck-us.net>
Signed-off-by: Rob Herring <robh at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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