SYSCTL: Add a mutex to the page_alloc zone order sysctl

The zone list code clearly cannot tolerate concurrent writers (I couldn't
find any locks for that), so simply add a global mutex. No need for RCU
in this case.

Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d79b92580561..4e9f5cc5fb59 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2402,13 +2402,14 @@ int numa_zonelist_order_handler(ctl_table *table, int write,
 {
         char saved_string[NUMA_ZONELIST_ORDER_LEN];
         int ret;
+        static DEFINE_MUTEX(zl_order_mutex);
 
+        mutex_lock(&zl_order_mutex);
         if (write)
-                strncpy(saved_string, (char*)table->data,
-                        NUMA_ZONELIST_ORDER_LEN);
+                strcpy(saved_string, (char*)table->data);
         ret = proc_dostring(table, write, buffer, length, ppos);
         if (ret)
-                return ret;
+                goto out;
         if (write) {
                 int oldval = user_zonelist_order;
                 if (__parse_numa_zonelist_order((char*)table->data)) {
@@ -2421,7 +2422,9 @@ int numa_zonelist_order_handler(ctl_table *table, int write,
                 } else if (oldval != user_zonelist_order)
                         build_all_zonelists();
         }
-        return 0;
+out:
+        mutex_unlock(&zl_order_mutex);
+        return ret;
 }