+ mm-migrate-fix-softlockup-in-do_pages_stat-with-huge-page-arrays.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/migrate: fix softlockup in do_pages_stat() with huge page arrays
has been added to the -mm mm-new branch.  Its filename is
     mm-migrate-fix-softlockup-in-do_pages_stat-with-huge-page-arrays.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-fix-softlockup-in-do_pages_stat-with-huge-page-arrays.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Qi Xi <xiqi2@huawei.com>
Subject: mm/migrate: fix softlockup in do_pages_stat() with huge page arrays
Date: Sat, 31 Oct 2026 11:33:30 +0800

do_pages_stat() walks the user page array in 16-page chunks but never
reschedules, so a huge nr_pages can hold a CPU past the watchdog threshold
on non-preemptible kernels.  Add cond_resched() to the loop so long
move_pages() node-query calls yield periodically.

With KASAN and function tracing enabled, a move_pages() node query (nodes
== NULL) over 10 million page entries (~40GB) can trigger the softlockup
on a PREEMPT_NONE kernel.

Link: https://lore.kernel.org/20261031033330.3416326-1-xiqi5703@163.com
Fixes: 80bba1290ab5 ("mm: no get_user/put_user while holding mmap_sem in do_pages_stat?")
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Qiliang Yuan <odys.yuan@gmail.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: <stable@vger.kernel.org>
---

 mm/migrate.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/migrate.c~mm-migrate-fix-softlockup-in-do_pages_stat-with-huge-page-arrays
+++ a/mm/migrate.c
@@ -2555,6 +2555,7 @@ static int do_pages_stat(struct mm_struc
 
 		chunk_offset += chunk_nr;
 		nr_pages -= chunk_nr;
+		cond_resched();
 	}
 	return nr_pages ? -EFAULT : 0;
 }
_

Patches currently in -mm which might be from xiqi2@huawei.com are

mm-migrate-fix-softlockup-in-do_pages_stat-with-huge-page-arrays.patch