Re: [PATCH 1/6] fs/proc/task_mmu: fix make_uffd_wp_huge_pte() prot-update race

[Breno Leitao]

Hello Kiryl,

On Fri, May 29, 2026 at 06:23:25PM +0100, Kiryl Shutsemau (Meta) wrote:
> The non-hugetlb sibling make_uffd_wp_pte() does this correctly via
> ptep_modify_prot_start() / ptep_modify_prot_commit(). Mirror that
> pattern for the present-PTE branch. The migration case stays as-is --
> migration entries are non-present, so there's no hardware update to
> race against.

I am  seeing this on next-20261109 (arm64, PAGE_TABLE_CHECK) while the
pagemap_ioctl kselftest runs next to a workload that migrates pages:

    WARNING: mm/page_table_check.c:206 at __page_table_check_ptes_set+0x168/0x178, CPU#21: pagemap_ioctl/894691
    Call trace:
     __page_table_check_ptes_set+0x168/0x178 (P)
     __set_ptes_anysz+0x50/0x240
     make_uffd_wp_pte+0x104/0x1c8
     pagemap_scan_pmd_entry+0x1b98/0x1df8
     walk_pgd_range+0x7b4/0xd00
     __walk_page_range+0x108/0x510
     walk_page_range_mm_unsafe+0x150/0x3e8
     do_pagemap_cmd+0x418/0x7d0
     __arm64_sys_ioctl+0xc08/0x1338

given you've touched this recently, I am wondering if you've seen it.

--breno