[PATCH 5.15.y 4/7] mm/kmemleak: prevent soft lockup in kmemleak_scan()'s object iteration loops

[Sasha Levin <sashal@kernel.org>]

From: Waiman Long <longman@redhat.com>

[ Upstream commit 984a608377cb623351b8a3670b285f32ebeb2d32 ]

Commit 6edda04ccc7c ("mm/kmemleak: prevent soft lockup in first object
iteration loop of kmemleak_scan()") adds cond_resched() in the first
object iteration loop of kmemleak_scan().  However, it turns that the 2nd
objection iteration loop can still cause soft lockup to happen in some
cases.  So add a cond_resched() call in the 2nd and 3rd loops as well to
prevent that and for completeness.

Link: https://lkml.kernel.org/r/20221020175619.366317-1-longman@redhat.com
Fixes: 6edda04ccc7c ("mm/kmemleak: prevent soft lockup in first object iteration loop of kmemleak_scan()")
Signed-off-by: Waiman Long <longman@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 5d10d4e19e6d ("mm/kmemleak: avoid soft lockup when scanning task stacks")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/kmemleak.c | 61 +++++++++++++++++++++++++++++++++++----------------
 1 file changed, 42 insertions(+), 19 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index e52f0cbed6f2b..b4d7c1deedc17 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1402,6 +1402,27 @@ static void scan_gray_list(void)
 	WARN_ON(!list_empty(&gray_list));
 }
 
+/*
+ * 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
+ */
+static bool kmemleak_cond_resched(struct kmemleak_object *object, bool pinned)
+{
+	if (!pinned && !get_object(object))
+		return false;
+
+	rcu_read_unlock();
+	cond_resched();
+	rcu_read_lock();
+	if (!pinned)
+		put_object(object);
+	return true;
+}
+
 /*
  * Scan data sections and all the referenced memory blocks allocated via the
  * kernel's standard allocators. This function must be called with the
@@ -1413,7 +1434,7 @@ static void kmemleak_scan(void)
 	struct zone *zone;
 	int __maybe_unused i;
 	int new_leaks = 0;
-	int loop1_cnt = 0;
+	int loop_cnt = 0;
 
 	jiffies_last_scan = jiffies;
 
@@ -1422,7 +1443,6 @@ static void kmemleak_scan(void)
 	list_for_each_entry_rcu(object, &object_list, object_list) {
 		bool obj_pinned = false;
 
-		loop1_cnt++;
 		raw_spin_lock_irq(&object->lock);
 #ifdef DEBUG
 		/*
@@ -1445,24 +1465,11 @@ static void kmemleak_scan(void)
 		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.
+		 * Do a cond_resched() every 64k objects to avoid soft lockup.
 		 */
-		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);
-		}
+		if (!(++loop_cnt & 0xffff) &&
+		    !kmemleak_cond_resched(object, obj_pinned))
+			loop_cnt--; /* Try again on next object */
 	}
 	rcu_read_unlock();
 
@@ -1529,7 +1536,15 @@ 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 */
+
 		/*
 		 * This is racy but we can save the overhead of lock/unlock
 		 * calls. The missed objects, if any, should be caught in
@@ -1563,7 +1578,15 @@ 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 */
+
 		/*
 		 * This is racy but we can save the overhead of lock/unlock
 		 * calls. The missed objects, if any, should be caught in
-- 
2.53.0