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>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d79b925..4e9f5cc 100644 (file)
--- 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;
 }