The patch titled Subject: mm/kmemleak: prevent soft lockup in kmemleak_scan()'s object iteration loops has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-kmemleak-prevent-soft-lockup-in-kmemleak_scans-object-iteration-loops.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days

------------------------------------------------------ From: Waiman Long longman@redhat.com Subject: mm/kmemleak: prevent soft lockup in kmemleak_scan()'s object iteration loops Date: Thu, 20 Oct 2022 13:56:19 -0400

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 ---

mm/kmemleak.c | 61 +++++++++++++++++++++++++++++++++--------------- 1 file changed, 42 insertions(+), 19 deletions(-)

--- a/mm/kmemleak.c~mm-kmemleak-prevent-soft-lockup-in-kmemleak_scans-object-iteration-loops +++ a/mm/kmemleak.c @@ -1461,6 +1461,27 @@ 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 + */ +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 * scan_mutex held. @@ -1471,7 +1492,7 @@ 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;

@@ -1480,7 +1501,6 @@ 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 /* @@ -1514,24 +1534,11 @@ 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();

@@ -1598,8 +1605,16 @@ 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 * the next scan. @@ -1632,8 +1647,16 @@ 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 * the next scan. _

Patches currently in -mm which might be from longman@redhat.com are

mm-kmemleak-prevent-soft-lockup-in-kmemleak_scans-object-iteration-loops.patch