Re: [PATCH] mm: memory: fix truncation removing mapped folios

[Lorenzo Stoakes (ARM)]

On Fri, Oct 09, 2026 at 06:12:03PM +0800, Baolin Wang wrote:
> diff --git a/mm/memory.c b/mm/memory.c
> index 1f5d5f7d39cd..0272217ad7b0 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c

> @@ -2044,16 +2053,10 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  	 * to ensure they are still none, thereby preventing the pte entries
>  	 * from being repopulated by another thread.
>  	 */
> -	if (can_reclaim_pt && direct_reclaim && addr == end)
> +	if (can_reclaim_pt && direct_reclaim && addr == end) {
> +		/* rmap changes need to be observed before e.g PTEs get zapped. */
> +		smp_wmb();

What does this pair with? You should always say what in the comment.

rmb/wmb are generally not needed vs. acquire/release. Are you sure a wmb is
right here?

--
Cheers, Lorenzo