+ mm-smaps-fix-race-between-smaps_hugetlb_range-and-migration.patch added to mm-new branch

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

The patch titled
     Subject: mm/smaps: fix race between smaps_hugetlb_range and migration
has been added to the -mm mm-new branch.  Its filename is
     mm-smaps-fix-race-between-smaps_hugetlb_range-and-migration.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-smaps-fix-race-between-smaps_hugetlb_range-and-migration.patch

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

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patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Jinjiang Tu <tujinjiang@huawei.com>
Subject: mm/smaps: fix race between smaps_hugetlb_range and migration
Date: Thu, 24 Jul 2025 17:09:56 +0800

Patch series "hold PTL for several .hugetlb_entry callbacks", v2.

Patch #1 fixes a race between smaps_hugetlb_range() and migration by
holding PTL in smaps_hugetlb_range().

To avoid operating on stale pages, add PTL for several .hugetlb_entry
callbacks too.  We don't hold PTL in __s390_enable_skey_hugetlb() and
prot_none_hugetlb_entry(), since the mmap write lock is held.  We don't
hold PTL in hwpoison_hugetlb_range() too, since it only reads the pte and
doesn't operate the page.


This patch (of 3):

smaps_hugetlb_range() handles the pte without holdling ptl, and may be
concurrenct with migration, leaing to BUG_ON in pfn_swap_entry_to_page(). 
The race is as follows.

smaps_hugetlb_range              migrate_pages
  huge_ptep_get
                                   remove_migration_ptes
				   folio_unlock
  pfn_swap_entry_folio
    BUG_ON

To fix it, hold ptl lock in smaps_hugetlb_range().

Link: https://lkml.kernel.org/r/20250724090958.455887-1-tujinjiang@huawei.com
Link: https://lkml.kernel.org/r/20250724090958.455887-2-tujinjiang@huawei.com
Fixes: 25ee01a2fca0 ("mm: hugetlb: proc: add hugetlb-related fields to /proc/PID/smaps")
Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Brahmajit Das <brahmajit.xyz@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Rientjes <rientjes@google.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joern Engel <joern@logfs.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/task_mmu.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/fs/proc/task_mmu.c~mm-smaps-fix-race-between-smaps_hugetlb_range-and-migration
+++ a/fs/proc/task_mmu.c
@@ -1148,10 +1148,13 @@ static int smaps_hugetlb_range(pte_t *pt
 {
 	struct mem_size_stats *mss = walk->private;
 	struct vm_area_struct *vma = walk->vma;
-	pte_t ptent = huge_ptep_get(walk->mm, addr, pte);
 	struct folio *folio = NULL;
 	bool present = false;
+	spinlock_t *ptl;
+	pte_t ptent;
 
+	ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);
+	ptent = huge_ptep_get(walk->mm, addr, pte);
 	if (pte_present(ptent)) {
 		folio = page_folio(pte_page(ptent));
 		present = true;
@@ -1170,6 +1173,7 @@ static int smaps_hugetlb_range(pte_t *pt
 		else
 			mss->private_hugetlb += huge_page_size(hstate_vma(vma));
 	}
+	spin_unlock(ptl);
 	return 0;
 }
 #else
_

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

mm-memory_hotplug-fix-hwpoisoned-large-folio-handling-in-do_migrate_range.patch
mm-smaps-fix-race-between-smaps_hugetlb_range-and-migration.patch
fs-proc-task_mmu-hold-ptl-in-pagemap_hugetlb_range-and-gather_hugetlb_stats.patch
mm-mincore-hold-ptl-in-mincore_hugetlb.patch