The patch titled Subject: mm/kmemleak: avoid soft lockup in __kmemleak_do_cleanup() has been added to the -mm mm-nonmm-unstable branch. Its filename is mm-kmemleak-avoid-soft-lockup-in-__kmemleak_do_cleanup.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-nonmm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Waiman Long longman@redhat.com Subject: mm/kmemleak: avoid soft lockup in __kmemleak_do_cleanup() Date: Mon, 28 Jul 2025 15:02:48 -0400
A soft lockup warning was observed on a relative small system x86-64 system with 16 GB of memory when running a debug kernel with kmemleak enabled.
watchdog: BUG: soft lockup - CPU#8 stuck for 33s! [kworker/8:1:134]
The test system was running a workload with hot unplug happening in parallel. Then kemleak decided to disable itself due to its inability to allocate more kmemleak objects. The debug kernel has its CONFIG_DEBUG_KMEMLEAK_MEM_POOL_SIZE set to 40,000.
The soft lockup happened in kmemleak_do_cleanup() when the existing kmemleak objects were being removed and deleted one-by-one in a loop via a workqueue. In this particular case, there are at least 40,000 objects that need to be processed and given the slowness of a debug kernel and the fact that a raw_spinlock has to be acquired and released in __delete_object(), it could take a while to properly handle all these objects.
As kmemleak has been disabled in this case, the object removal and deletion process can be further optimized as locking isn't really needed. However, it is probably not worth the effort to optimize for such an edge case that should rarely happen. So the simple solution is to call cond_resched() at periodic interval in the iteration loop to avoid soft lockup.
Link: https://lkml.kernel.org/r/20250728190248.605750-1-longman@redhat.com Signed-off-by: Waiman Long longman@redhat.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/kmemleak.c | 5 +++++ 1 file changed, 5 insertions(+)
--- a/mm/kmemleak.c~mm-kmemleak-avoid-soft-lockup-in-__kmemleak_do_cleanup +++ a/mm/kmemleak.c @@ -2181,6 +2181,7 @@ static const struct file_operations kmem static void __kmemleak_do_cleanup(void) { struct kmemleak_object *object, *tmp; + unsigned int cnt = 0;
/* * Kmemleak has already been disabled, no need for RCU list traversal @@ -2189,6 +2190,10 @@ static void __kmemleak_do_cleanup(void) list_for_each_entry_safe(object, tmp, &object_list, object_list) { __remove_object(object); __delete_object(object); + + /* Call cond_resched() once per 64 iterations to avoid soft lockup */ + if (!(++cnt & 0x3f)) + cond_resched(); } }
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Patches currently in -mm which might be from longman@redhat.com are
mm-kmemleak-avoid-soft-lockup-in-__kmemleak_do_cleanup.patch