4 files changed, 23 insertions, 2 deletions

diff --git a/include/linux/oom.h b/include/linux/oom.h
index 13b7b02e599a..6f9d04a85336 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -40,6 +40,7 @@ enum oom_constraint {
         CONSTRAINT_MEMCG,
 };
 
+extern void compare_swap_oom_score_adj(int old_val, int new_val);
 extern int test_set_oom_score_adj(int new_val);
 
 extern unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
diff --git a/mm/ksm.c b/mm/ksm.c
index 9a68b0cf0a1c..310544a379ae 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1905,7 +1905,8 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
 
                         oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
                         err = unmerge_and_remove_all_rmap_items();
-                        test_set_oom_score_adj(oom_score_adj);
+                        compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
+                                                                oom_score_adj);
                         if (err) {
                                 ksm_run = KSM_RUN_STOP;
                                 count = err;
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 2b97e8f04607..e916168b6e0a 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -39,6 +39,25 @@ int sysctl_oom_kill_allocating_task;
 int sysctl_oom_dump_tasks = 1;
 static DEFINE_SPINLOCK(zone_scan_lock);
 
+/*
+ * compare_swap_oom_score_adj() - compare and swap current's oom_score_adj
+ * @old_val: old oom_score_adj for compare
+ * @new_val: new oom_score_adj for swap
+ *
+ * Sets the oom_score_adj value for current to @new_val iff its present value is
+ * @old_val.  Usually used to reinstate a previous value to prevent racing with
+ * userspacing tuning the value in the interim.
+ */
+void compare_swap_oom_score_adj(int old_val, int new_val)
+{
+        struct sighand_struct *sighand = current->sighand;
+
+        spin_lock_irq(&sighand->siglock);
+        if (current->signal->oom_score_adj == old_val)
+                current->signal->oom_score_adj = new_val;
+        spin_unlock_irq(&sighand->siglock);
+}
+
 /**
  * test_set_oom_score_adj() - set current's oom_score_adj and return old value
  * @new_val: new oom_score_adj value
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 17bc224bce68..c9d654009125 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1617,7 +1617,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 
         oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
         err = try_to_unuse(type);
-        test_set_oom_score_adj(oom_score_adj);
+        compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX, oom_score_adj);
 
         if (err) {
                 /*