linux-kernel - [PATCH 1/2] mm/kmemleak: Simplify kmemleak_cond

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Date:   Sat, 10 Dec 2022 18:00:47 -0500
From:   Waiman Long <longman@...hat.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH 1/2] mm/kmemleak: Simplify kmemleak_cond_resched() usage

The presence of a pinned argument and the 64k loop count make
kmemleak_cond_resched() a bit more complex to read. The pinned argument
is used only by first kmemleak_scan() loop.

Simplify the usage of kmemleak_cond_resched() by removing the pinned
argument and always do a get_object()/put_object() sequence. In
addition, the 64k loop is removed by using need_resched() to decide if
kmemleak_cond_resched() should be called.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 mm/kmemleak.c | 48 ++++++++++++------------------------------------
 1 file changed, 12 insertions(+), 36 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 646e2979641f..8c44f70ed457 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1463,22 +1463,17 @@ static void scan_gray_list(void)
 /*
  * Conditionally call resched() in a object iteration loop while making sure
  * that the given object won't go away without RCU read lock by performing a
- * get_object() if !pinned.
- *
- * Return: false if can't do a cond_resched() due to get_object() failure
- *	   true otherwise
+ * get_object() if necessaary.
  */
-static bool kmemleak_cond_resched(struct kmemleak_object *object, bool pinned)
+static void kmemleak_cond_resched(struct kmemleak_object *object)
 {
-	if (!pinned && !get_object(object))
-		return false;
+	if (!get_object(object))
+		return;	/* Try next object */
 
 	rcu_read_unlock();
 	cond_resched();
 	rcu_read_lock();
-	if (!pinned)
-		put_object(object);
-	return true;
+	put_object(object);
 }
 
 /*
@@ -1492,15 +1487,12 @@ static void kmemleak_scan(void)
 	struct zone *zone;
 	int __maybe_unused i;
 	int new_leaks = 0;
-	int loop_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;
-
 		raw_spin_lock_irq(&object->lock);
 #ifdef DEBUG
 		/*
@@ -1526,19 +1518,13 @@ 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() every 64k objects to avoid soft lockup.
-		 */
-		if (!(++loop_cnt & 0xffff) &&
-		    !kmemleak_cond_resched(object, obj_pinned))
-			loop_cnt--; /* Try again on next object */
+		if (need_resched())
+			kmemleak_cond_resched(object);
 	}
 	rcu_read_unlock();
 
@@ -1605,14 +1591,9 @@ static void kmemleak_scan(void)
 	 * scan and color them gray until the next scan.
 	 */
 	rcu_read_lock();
-	loop_cnt = 0;
 	list_for_each_entry_rcu(object, &object_list, object_list) {
-		/*
-		 * Do a cond_resched() every 64k objects to avoid soft lockup.
-		 */
-		if (!(++loop_cnt & 0xffff) &&
-		    !kmemleak_cond_resched(object, false))
-			loop_cnt--;	/* Try again on next object */
+		if (need_resched())
+			kmemleak_cond_resched(object);
 
 		/*
 		 * This is racy but we can save the overhead of lock/unlock
@@ -1647,14 +1628,9 @@ static void kmemleak_scan(void)
 	 * Scanning result reporting.
 	 */
 	rcu_read_lock();
-	loop_cnt = 0;
 	list_for_each_entry_rcu(object, &object_list, object_list) {
-		/*
-		 * Do a cond_resched() every 64k objects to avoid soft lockup.
-		 */
-		if (!(++loop_cnt & 0xffff) &&
-		    !kmemleak_cond_resched(object, false))
-			loop_cnt--;	/* Try again on next object */
+		if (need_resched())
+			kmemleak_cond_resched(object);
 
 		/*
 		 * This is racy but we can save the overhead of lock/unlock
-- 
2.31.1