oom incremental fixes

@@ -386,9 +386,6 @@ void out_of_memory(struct zonelist *zone
 		/* Got some memory back in the last second. */
 		return;
 
-	if (down_trylock(&OOM_lock))
-		return;
-
 	if (sysctl_panic_on_oom == 2)
 		panic("out of memory. Compulsory panic_on_oom is selected.\n");
 

@@ -398,32 +395,39 @@ void out_of_memory(struct zonelist *zone
 	 */
 	constraint = constrained_alloc(zonelist, gfp_mask);
 	cpuset_lock();
-	read_lock(&tasklist_lock);
-
-	/*
-	 * This holds the down(OOM_lock)+read_lock(tasklist_lock), so it's
-	 * equivalent to write_lock_irq(tasklist_lock) as far as VM_is_OOM
-	 * is concerned.
-	 */
-	if (unlikely(test_bit(0, &VM_is_OOM))) {
-		if (time_before(jiffies, last_tif_memdie_jiffies + 10*HZ))
-			goto out;
-		printk("detected probable OOM deadlock, so killing another task\n");
-		last_tif_memdie_jiffies = jiffies;
-	}
 
 	switch (constraint) {
 	case CONSTRAINT_MEMORY_POLICY:
+		read_lock(&tasklist_lock);
 		oom_kill_process(current, points,
 				 "No available memory (MPOL_BIND)", gfp_mask, order);
+		read_unlock(&tasklist_lock);
 		break;
 
 	case CONSTRAINT_CPUSET:
+		read_lock(&tasklist_lock);
 		oom_kill_process(current, points,
 				 "No available memory in cpuset", gfp_mask, order);
+		read_unlock(&tasklist_lock);
 		break;
 
 	case CONSTRAINT_NONE:
+		if (down_trylock(&OOM_lock))
+			break;
+		read_lock(&tasklist_lock);
+
+		/*
+		 * This holds the down(OOM_lock)+read_lock(tasklist_lock),
+		 * so it's equivalent to write_lock_irq(tasklist_lock) as
+		 * far as VM_is_OOM is concerned.
+		 */
+		if (unlikely(test_bit(0, &VM_is_OOM))) {
+			if (time_before(jiffies, last_tif_memdie_jiffies + 10*HZ))
+				goto out;
+			printk("detected probable OOM deadlock, so killing another task\n");
+			last_tif_memdie_jiffies = jiffies;
+		}
+
 		if (sysctl_panic_on_oom)
 			panic("out of memory. panic_on_oom is selected\n");
 retry:

@@ -442,12 +446,11 @@ retry:
 		if (oom_kill_process(p, points, "Out of memory", gfp_mask, order))
 			goto retry;
 
+	out:
+		read_unlock(&tasklist_lock);
+		up(&OOM_lock);
 		break;
 	}
 
-out:
-	read_unlock(&tasklist_lock);
 	cpuset_unlock();
-
-	up(&OOM_lock);
-}
+}

@@ -428,8 +428,11 @@ void out_of_memory(struct zonelist *zone
 			last_tif_memdie_jiffies = jiffies;
 		}
 
-		if (sysctl_panic_on_oom)
+		if (sysctl_panic_on_oom) {
+			read_unlock(&tasklist_lock);
+			cpuset_unlock();
 			panic("out of memory. panic_on_oom is selected\n");
+		}
 retry:
 		/*
 		 * Rambo mode: Shoot down a process and hope it solves whatever

@@ -437,7 +440,7 @@ retry:
 		 */
 		p = select_bad_process(&points);
 		/* Found nothing?!?! Either we hang forever, or we panic. */
-		if (!p) {
+		if (unlikely(!p)) {
 			read_unlock(&tasklist_lock);
 			cpuset_unlock();
 			panic("Out of memory and no killable processes...\n");