The patch titled
Subject: mm/kmemleak: use _irq lock/unlock variants in kmemleak_scan/_clear()
has been added to the -mm mm-unstable branch. Its filename is
mm-kmemleak-use-_irq-lock-unlock-variants-in-kmemleak_scan-_clear.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmemleak-use-_irq-lock-unlock-variants-in-kmemleak_scan-_clear.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: use _irq lock/unlock variants in kmemleak_scan/_clear()
Date: Sun, 12 Jun 2022 14:32:59 -0400
Patch series "mm/kmemleak: Avoid soft lockup in kmemleak_scan()".
There are 3 RCU-based object iteration loops in kmemleak_scan(). Because
of the need to take RCU read lock, we can't insert cond_resched() into the
loop like other parts of the function. As there can be millions of
objects to be scanned, it takes a while to iterate all of them. The
kmemleak functionality is usually enabled in a debug kernel which is much
slower than a non-debug kernel. With sufficient number of kmemleak
objects, the time to iterate them all may exceed 22s causing soft lockup.
watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [kmemleak:625]
This patch series make changes to the 3 object iteration loops in
kmemleak_scan() to prevent them from causing soft lockup.
This patch (of 3);
kmemleak_scan() is called only from the kmemleak scan thread or from write
to the kmemleak debugfs file. Both are in task context and so we can
directly use the simpler _irq() lock/unlock calls instead of the more
complex _irqsave/_irqrestore variants.
Similarly, kmemleak_clear() is called only from write to the kmemleak
debugfs file. The same change can be applied.
Link: https://lkml.kernel.org/r/20220612183301.981616-1-longman@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20220612183301.981616-2-longman@xxxxxxxxxx
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kmemleak.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
--- a/mm/kmemleak.c~mm-kmemleak-use-_irq-lock-unlock-variants-in-kmemleak_scan-_clear
+++ a/mm/kmemleak.c
@@ -1470,7 +1470,6 @@ static void scan_gray_list(void)
*/
static void kmemleak_scan(void)
{
- unsigned long flags;
struct kmemleak_object *object;
struct zone *zone;
int __maybe_unused i;
@@ -1481,7 +1480,7 @@ static void kmemleak_scan(void)
/* prepare the kmemleak_object's */
rcu_read_lock();
list_for_each_entry_rcu(object, &object_list, object_list) {
- raw_spin_lock_irqsave(&object->lock, flags);
+ raw_spin_lock_irq(&object->lock);
#ifdef DEBUG
/*
* With a few exceptions there should be a maximum of
@@ -1509,7 +1508,7 @@ static void kmemleak_scan(void)
if (color_gray(object) && get_object(object))
list_add_tail(&object->gray_list, &gray_list);
- raw_spin_unlock_irqrestore(&object->lock, flags);
+ raw_spin_unlock_irq(&object->lock);
}
rcu_read_unlock();
@@ -1577,14 +1576,14 @@ static void kmemleak_scan(void)
*/
rcu_read_lock();
list_for_each_entry_rcu(object, &object_list, object_list) {
- raw_spin_lock_irqsave(&object->lock, flags);
+ raw_spin_lock_irq(&object->lock);
if (color_white(object) && (object->flags & OBJECT_ALLOCATED)
&& update_checksum(object) && get_object(object)) {
/* color it gray temporarily */
object->count = object->min_count;
list_add_tail(&object->gray_list, &gray_list);
}
- raw_spin_unlock_irqrestore(&object->lock, flags);
+ raw_spin_unlock_irq(&object->lock);
}
rcu_read_unlock();
@@ -1604,7 +1603,7 @@ static void kmemleak_scan(void)
*/
rcu_read_lock();
list_for_each_entry_rcu(object, &object_list, object_list) {
- raw_spin_lock_irqsave(&object->lock, flags);
+ raw_spin_lock_irq(&object->lock);
if (unreferenced_object(object) &&
!(object->flags & OBJECT_REPORTED)) {
object->flags |= OBJECT_REPORTED;
@@ -1614,7 +1613,7 @@ static void kmemleak_scan(void)
new_leaks++;
}
- raw_spin_unlock_irqrestore(&object->lock, flags);
+ raw_spin_unlock_irq(&object->lock);
}
rcu_read_unlock();
@@ -1816,15 +1815,14 @@ static int dump_str_object_info(const ch
static void kmemleak_clear(void)
{
struct kmemleak_object *object;
- unsigned long flags;
rcu_read_lock();
list_for_each_entry_rcu(object, &object_list, object_list) {
- raw_spin_lock_irqsave(&object->lock, flags);
+ raw_spin_lock_irq(&object->lock);
if ((object->flags & OBJECT_REPORTED) &&
unreferenced_object(object))
__paint_it(object, KMEMLEAK_GREY);
- raw_spin_unlock_irqrestore(&object->lock, flags);
+ raw_spin_unlock_irq(&object->lock);
}
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
