Re: [PATCH v2] mm: avoid KCSAN false positive in memdesc_nid()

[David Hildenbrand (Arm)]

On 6/23/26 10:44, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@xxxxxxxxxx>
> 
> KCSAN reports a data race between page_to_nid()/folio_nid() reading
> page->flags and folio_trylock()/folio_lock() concurrently doing
> test_and_set_bit_lock(PG_locked, ...) on the same word, e.g.:
> 
>   BUG: KCSAN: data-race in __lruvec_stat_mod_folio / shmem_get_folio_gfp
> 
> The node id occupies a fixed bit-range of page->flags that is set
> once at page init and never modified afterwards, so it can never
> overlap with the low PG_locked/PG_waiters bits touched by the folio
> lock path.
> 
> Use ASSERT_EXCLUSIVE_BITS() in memdesc_nid() to scope the exemption
> to just the node-id bits, consistent with how memdesc_zonenum()
> already handles the same class of race for the zone-id bits.
> 
> Signed-off-by: Hui Zhu <zhuhui@xxxxxxxxxx>
> ---

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David