Re: [PATCH 0/2] mm/slab: fix lockdep warnings with kmalloc_nolock()

[Vlastimil Babka <vbabka@suse.cz>]

On 2/6/26 18:37, Harry Yoo wrote:
> On Sat, Feb 07, 2026 at 02:13:46AM +0900, Harry Yoo wrote:
>> Hi, I've observed a tw lockdep warnings while testing
>> kmalloc_nolock() in NMI:
>> 
>>   1. Accessing current->mems_allowed_seq seqlock in NMI isn't safe
>>      and lockdep complains.
>> 
>>   2. w/ CONFIG_SLAB_FREELIST_RANDOM, get_random_u32() acquires
>>      a local_lock, which isn't safe in NMI and could cause a deadlock.
>> 
>> Let's fix them.
> 
> I think we should probably add some sort of
> kmalloc_nolock()/kfree_nolock() test cases in lib/tests/slub_kunit.c.

That would be useful, yes!

> These haven't been discovered by bots because (I guess) it is very
> unlikely for bots to somehow trigger those APIs in NMI.
> 
> Also, I forgot to mention that this is based on slab/for-next:
> 
> commit bc33906024eb5955294e28128c3d0f492d2ded5e
> Merge: ec15c383fcda 40fd0acc45d0
> Author: Vlastimil Babka <vbabka@suse.cz>
> Date:   Thu Jan 29 10:10:50 2026 +0100
> 
>     Merge branch 'slab/for-7.0/sheaves' into slab/for-next
> 
>> Harry Yoo (2):
>>   mm/slab: skip get_from_any_partial() if !allow_spin
>>   mm/slab: use prandom if !allow_spin
>> 
>>  mm/slub.c | 36 ++++++++++++++++++++++++++++++++----
>>  1 file changed, 32 insertions(+), 4 deletions(-)
>> 
>> -- 
>> 2.43.0
>> 
>