mm/smaps: fix race between smaps_hugetlb_range and migration

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>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 3d6d8a9f13fc1856732a939913b40da81f046645..55bab10bc779aeac9103a1fee059dbb3b45d788d 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1148,10 +1148,13 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
 {
        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 *pte, unsigned long hmask,
                else
                        mss->private_hugetlb += huge_page_size(hstate_vma(vma));
        }
+       spin_unlock(ptl);
        return 0;
 }
 #else