Re: [PATCH V2 0/2] fix lockdep warnings with kmalloc_nolock()

[Vlastimil Babka <vbabka@suse.cz>]

On 2/10/26 09:18, Harry Yoo wrote:
> Hi, I've observed two 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.
> 
> Note: This is based on the latest slab/for-next. It wasn't clear to me
> if I should base it on slab/for-next or slab/for-next-fixes,
> because the merge window has started, this series needs some exposure
> in -next, and the patches in slab/for-next might land in mainline
> in the meantime.

Right, adding to slab/for-next on top of the submitted PR, so I can send
another next week. Thanks!

> But the conflict resolution should be trivial even if it should have
> been based on slab/for-next-fixes.
> 
> v1 -> v2:
>   - Patch 1: per Vlastimil's suggestion, do not access
>     current->mems_allowed_seq and avoid retry if !allow_spin,
>     rather than returning NULL.
> 
> v1: https://lore.kernel.org/linux-mm/20260206171348.35886-1-harry.yoo@oracle.com
> 
> Harry Yoo (2):
>   mm/slab: do not access current->mems_allowed_seq if !allow_spin
>   mm/slab: use prandom if !allow_spin
> 
>  mm/slub.c | 41 +++++++++++++++++++++++++++++++++++------
>  1 file changed, 35 insertions(+), 6 deletions(-)
> 
> 
> base-commit: f6ed7e47c1fc78e78c9bfeb668b1ad9ba5c58120
>