[PATCH 4/9] v4 Add mutex for add/remove of memory blocks

[Nathan Fontenot <nfont@austin.ibm.com>]

Add a new mutex for use in adding and removing of memory blocks.  This
is needed to avoid any race conditions in which the same memory block could
be added and removed at the same time.

Signed-off-by: Nathan Fontenot <nfont@austin.ibm.com>
---
 drivers/base/memory.c |    9 +++++++++
 1 file changed, 9 insertions(+)

Index: linux-2.6/drivers/base/memory.c
===================================================================
--- linux-2.6.orig/drivers/base/memory.c	2010-08-02 13:35:00.000000000 -0500
+++ linux-2.6/drivers/base/memory.c	2010-08-02 13:45:34.000000000 -0500
@@ -27,6 +27,8 @@
 #include <asm/atomic.h>
 #include <asm/uaccess.h>
 
+static struct mutex mem_sysfs_mutex;
+
 #define MEMORY_CLASS_NAME	"memory"
 
 static struct sysdev_class memory_sysdev_class = {
@@ -485,6 +487,8 @@ static int add_memory_block(int nid, str
 	if (!mem)
 		return -ENOMEM;
 
+	mutex_lock(&mem_sysfs_mutex);
+
 	mem->start_phys_index = __section_nr(section);
 	mem->state = state;
 	atomic_inc(&mem->section_count);
@@ -508,6 +512,7 @@ static int add_memory_block(int nid, str
 			ret = register_mem_sect_under_node(mem, nid);
 	}
 
+	mutex_unlock(&mem_sysfs_mutex);
 	return ret;
 }
 
@@ -516,6 +521,7 @@ int remove_memory_block(unsigned long no
 {
 	struct memory_block *mem;
 
+	mutex_lock(&mem_sysfs_mutex);
 	mem = find_memory_block(section);
 
 	if (atomic_dec_and_test(&mem->section_count)) {
@@ -528,6 +534,7 @@ int remove_memory_block(unsigned long no
 		unregister_memory(mem, section);
 	}
 
+	mutex_unlock(&mem_sysfs_mutex);
 	return 0;
 }
 
@@ -562,6 +569,8 @@ int __init memory_dev_init(void)
 	if (ret)
 		goto out;
 
+	mutex_init(&mem_sysfs_mutex);
+
 	/*
 	 * Create entries for memory sections that were found
 	 * during boot and have been initialized