mm/oom_kill: remove weird use of ERR_PTR()/PTR_ERR().

The normal expectation for ERR_PTR() is to put a negative errno into a
pointer.  oom_kill puts the magic -1 in the result (and has since
pre-git), which is probably clearer with an explicit cast.

Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

mm/oom_kill.c

@@ -288,7 +288,7 @@ enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
 
 /*
  * Simple selection loop. We chose the process with the highest
- * number of 'points'.
+ * number of 'points'.  Returns -1 on scan abort.
  *
  * (not docbooked, we don't want this one cluttering up the manual)
  */
@@ -314,7 +314,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
 			continue;
 		case OOM_SCAN_ABORT:
 			rcu_read_unlock();
-			return ERR_PTR(-1UL);
+			return (struct task_struct *)(-1UL);
 		case OOM_SCAN_OK:
 			break;
 		};
@@ -657,7 +657,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 		dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
 		panic("Out of memory and no killable processes...\n");
 	}
-	if (PTR_ERR(p) != -1UL) {
+	if (p != (void *)-1UL) {
 		oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
 				 nodemask, "Out of memory");
 		killed = 1;