The patch titled
Subject: mm/kmemleak: prevent soft lockup in first object iteration loop of kmemleak_scan()
has been added to the -mm mm-unstable branch. Its filename is
mm-kmemleak-prevent-soft-lockup-in-first-object-iteration-loop-of-kmemleak_scan.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmemleak-prevent-soft-lockup-in-first-object-iteration-loop-of-kmemleak_scan.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Waiman Long <longman@xxxxxxxxxx>
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/20220614220359.59282-4-longman@xxxxxxxxxx
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kmemleak.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
--- a/mm/kmemleak.c~mm-kmemleak-prevent-soft-lockup-in-first-object-iteration-loop-of-kmemleak_scan
+++ a/mm/kmemleak.c
@@ -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 longman@xxxxxxxxxx are
mm-kmemleak-use-_irq-lock-unlock-variants-in-kmemleak_scan-_clear.patch
mm-kmemleak-skip-unlikely-objects-in-kmemleak_scan-without-taking-lock.patch
mm-kmemleak-prevent-soft-lockup-in-first-object-iteration-loop-of-kmemleak_scan.patch
