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.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
mm/kmemleak.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 7dd64139a7c7..abba063ae5ee 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1417,12 +1417,16 @@ 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
/*
@@ -1437,10 +1441,32 @@ static void kmemleak_scan(void)
#endif
/* 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();
--
2.31.1
