mm/kmemleak: use _irq lock/unlock variants in kmemleak_scan/_clear()

Patch series "mm/kmemleak: Avoid soft lockup in kmemleak_scan()", v2.

There are 3 RCU-based object iteration loops in kmemleak_scan().  Because
of the need to take RCU read lock, we can't insert cond_resched() into the
loop like other parts of the function.  As there can be millions of
objects to be scanned, it takes a while to iterate all of them.  The
kmemleak functionality is usually enabled in a debug kernel which is much
slower than a non-debug kernel.  With sufficient number of kmemleak
objects, the time to iterate them all may exceed 22s causing soft lockup.

  watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [kmemleak:625]

This patch series make changes to the 3 object iteration loops in
kmemleak_scan() to prevent them from causing soft lockup.


This patch (of 3):

kmemleak_scan() is called only from the kmemleak scan thread or from write
to the kmemleak debugfs file.  Both are in task context and so we can
directly use the simpler _irq() lock/unlock calls instead of the more
complex _irqsave/_irqrestore variants.

Similarly, kmemleak_clear() is called only from write to the kmemleak
debugfs file. The same change can be applied.

Link: https://lkml.kernel.org/r/20220614220359.59282-1-longman@redhat.com
Link: https://lkml.kernel.org/r/20220614220359.59282-2-longman@redhat.com
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/kmemleak.c

@@ -1470,7 +1470,6 @@ static void scan_gray_list(void)
  */
 static void kmemleak_scan(void)
 {
-	unsigned long flags;
 	struct kmemleak_object *object;
 	struct zone *zone;
 	int __maybe_unused i;
@@ -1481,7 +1480,7 @@ static void kmemleak_scan(void)
 	/* prepare the kmemleak_object's */
 	rcu_read_lock();
 	list_for_each_entry_rcu(object, &object_list, object_list) {
-		raw_spin_lock_irqsave(&object->lock, flags);
+		raw_spin_lock_irq(&object->lock);
 #ifdef DEBUG
 		/*
 		 * With a few exceptions there should be a maximum of
@@ -1509,7 +1508,7 @@ static void kmemleak_scan(void)
 		if (color_gray(object) && get_object(object))
 			list_add_tail(&object->gray_list, &gray_list);
 
-		raw_spin_unlock_irqrestore(&object->lock, flags);
+		raw_spin_unlock_irq(&object->lock);
 	}
 	rcu_read_unlock();
 
@@ -1577,14 +1576,14 @@ static void kmemleak_scan(void)
 	 */
 	rcu_read_lock();
 	list_for_each_entry_rcu(object, &object_list, object_list) {
-		raw_spin_lock_irqsave(&object->lock, flags);
+		raw_spin_lock_irq(&object->lock);
 		if (color_white(object) && (object->flags & OBJECT_ALLOCATED)
 		    && update_checksum(object) && get_object(object)) {
 			/* color it gray temporarily */
 			object->count = object->min_count;
 			list_add_tail(&object->gray_list, &gray_list);
 		}
-		raw_spin_unlock_irqrestore(&object->lock, flags);
+		raw_spin_unlock_irq(&object->lock);
 	}
 	rcu_read_unlock();
 
@@ -1604,7 +1603,7 @@ static void kmemleak_scan(void)
 	 */
 	rcu_read_lock();
 	list_for_each_entry_rcu(object, &object_list, object_list) {
-		raw_spin_lock_irqsave(&object->lock, flags);
+		raw_spin_lock_irq(&object->lock);
 		if (unreferenced_object(object) &&
 		    !(object->flags & OBJECT_REPORTED)) {
 			object->flags |= OBJECT_REPORTED;
@@ -1614,7 +1613,7 @@ static void kmemleak_scan(void)
 
 			new_leaks++;
 		}
-		raw_spin_unlock_irqrestore(&object->lock, flags);
+		raw_spin_unlock_irq(&object->lock);
 	}
 	rcu_read_unlock();
 
@@ -1816,15 +1815,14 @@ static int dump_str_object_info(const char *str)
 static void kmemleak_clear(void)
 {
 	struct kmemleak_object *object;
-	unsigned long flags;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(object, &object_list, object_list) {
-		raw_spin_lock_irqsave(&object->lock, flags);
+		raw_spin_lock_irq(&object->lock);
 		if ((object->flags & OBJECT_REPORTED) &&
 		    unreferenced_object(object))
 			__paint_it(object, KMEMLEAK_GREY);
-		raw_spin_unlock_irqrestore(&object->lock, flags);
+		raw_spin_unlock_irq(&object->lock);
 	}
 	rcu_read_unlock();