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

[Harry Yoo <harry.yoo@oracle.com>]

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.

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
> 

-- 
Cheers,
Harry / Hyeonggon