mm-kmemleak-prevent-soft-lockup-in-first-object-iteration-loop-of-kmemleak_scan.patch removed from -mm tree

merged mm-stable Andrew Morton 1 participant 1 message Jun 17, 2022

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Andrew Morton

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2022-06-17 02:50 UTC #0 lore raw

The quilt patch titled
Subject: mm/kmemleak: prevent soft lockup in first object iteration loop of kmemleak_scan()
has been removed from the -mm tree. Its filename was
mm-kmemleak-prevent-soft-lockup-in-first-object-iteration-loop-of-kmemleak_scan.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Waiman Long <[email protected]>
Subject: mm/kmemleak: prevent soft lockup in first object iteration loop of kmemleak_scan()
Date: Tue, 14 Jun 2022 18:03:59 -0400

The first RCU-based object iteration loop has to modify the object count. So we cannot skip taking the object lock.

One way to avoid soft lockup is to insert occasional cond_resched() call into the loop. This cannot be done while holding the RCU read lock which is to protect objects from being freed. However, taking a reference to the object will prevent it from being freed. We can then do a cond_resched() call after every 64k objects safely.

Link https://lkml.kernel.org/r/[email protected] open here

Signed-off-by Waiman Long <[email protected]>

Reviewed-by Catalin Marinas <[email protected]>

Cc Muchun Song <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

---

 mm/kmemleak.c |   28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

mm/kmemleak.c renamed from mm/kmemleak.c~mm-kmemleak-prevent-soft-lockup-in-first-object-iteration-loop-of-kmemleak_scan +27 -1

@@ -1474,12 +1474,16 @@ static void kmemleak_scan(void)
 	struct zone *zone;
 	int __maybe_unused i;
 	int new_leaks = 0;
+	int loop1_cnt = 0;
 
 	jiffies_last_scan = jiffies;
 
 	/* prepare the kmemleak_object's */
 	rcu_read_lock();
 	list_for_each_entry_rcu(object, &object_list, object_list) {
+		bool obj_pinned = false;
+
+		loop1_cnt++;
 		raw_spin_lock_irq(&object->lock);
 #ifdef DEBUG
 		/*

@@ -1505,10 +1509,32 @@ static void kmemleak_scan(void)
 
 		/* reset the reference count (whiten the object) */
 		object->count = 0;
-		if (color_gray(object) && get_object(object))
+		if (color_gray(object) && get_object(object)) {
 			list_add_tail(&object->gray_list, &gray_list);
+			obj_pinned = true;
+		}
 
 		raw_spin_unlock_irq(&object->lock);
+
+		/*
+		 * Do a cond_resched() to avoid soft lockup every 64k objects.
+		 * Make sure a reference has been taken so that the object
+		 * won't go away without RCU read lock.
+		 */
+		if (!(loop1_cnt & 0xffff)) {
+			if (!obj_pinned && !get_object(object)) {
+				/* Try the next object instead */
+				loop1_cnt--;
+				continue;
+			}
+
+			rcu_read_unlock();
+			cond_resched();
+			rcu_read_lock();
+
+			if (!obj_pinned)
+				put_object(object);
+		}
 	}
 	rcu_read_unlock();

Patches currently in -mm which might be from [email protected] are