1 files changed, 31 insertions, 9 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 18f8c3acbb85..6e97ed775074 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -440,7 +440,8 @@ static void smaps_page_accumulate(struct mem_size_stats *mss,
 }
 
 static void smaps_account(struct mem_size_stats *mss, struct page *page,
-		bool compound, bool young, bool dirty, bool locked)
+		bool compound, bool young, bool dirty, bool locked,
+		bool migration)
 {
 	int i, nr = compound ? compound_nr(page) : 1;
 	unsigned long size = nr * PAGE_SIZE;
@@ -467,8 +468,15 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
 	 * page_count(page) == 1 guarantees the page is mapped exactly once.
 	 * If any subpage of the compound page mapped with PTE it would elevate
 	 * page_count().
+	 *
+	 * The page_mapcount() is called to get a snapshot of the mapcount.
+	 * Without holding the page lock this snapshot can be slightly wrong as
+	 * we cannot always read the mapcount atomically.  It is not safe to
+	 * call page_mapcount() even with PTL held if the page is not mapped,
+	 * especially for migration entries.  Treat regular migration entries
+	 * as mapcount == 1.
 	 */
-	if (page_count(page) == 1) {
+	if ((page_count(page) == 1) || migration) {
 		smaps_page_accumulate(mss, page, size, size << PSS_SHIFT, dirty,
 			locked, true);
 		return;
@@ -517,6 +525,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 	struct vm_area_struct *vma = walk->vma;
 	bool locked = !!(vma->vm_flags & VM_LOCKED);
 	struct page *page = NULL;
+	bool migration = false;
 
 	if (pte_present(*pte)) {
 		page = vm_normal_page(vma, addr, *pte);
@@ -536,8 +545,11 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 			} else {
 				mss->swap_pss += (u64)PAGE_SIZE << PSS_SHIFT;
 			}
-		} else if (is_pfn_swap_entry(swpent))
+		} else if (is_pfn_swap_entry(swpent)) {
+			if (is_migration_entry(swpent))
+				migration = true;
 			page = pfn_swap_entry_to_page(swpent);
+		}
 	} else {
 		smaps_pte_hole_lookup(addr, walk);
 		return;
@@ -546,7 +558,8 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 	if (!page)
 		return;
 
-	smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte), locked);
+	smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
+		      locked, migration);
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
@@ -557,6 +570,7 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
 	struct vm_area_struct *vma = walk->vma;
 	bool locked = !!(vma->vm_flags & VM_LOCKED);
 	struct page *page = NULL;
+	bool migration = false;
 
 	if (pmd_present(*pmd)) {
 		/* FOLL_DUMP will return -EFAULT on huge zero page */
@@ -564,8 +578,10 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
 	} else if (unlikely(thp_migration_supported() && is_swap_pmd(*pmd))) {
 		swp_entry_t entry = pmd_to_swp_entry(*pmd);
 
-		if (is_migration_entry(entry))
+		if (is_migration_entry(entry)) {
+			migration = true;
 			page = pfn_swap_entry_to_page(entry);
+		}
 	}
 	if (IS_ERR_OR_NULL(page))
 		return;
@@ -577,7 +593,9 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
 		/* pass */;
 	else
 		mss->file_thp += HPAGE_PMD_SIZE;
-	smaps_account(mss, page, true, pmd_young(*pmd), pmd_dirty(*pmd), locked);
+
+	smaps_account(mss, page, true, pmd_young(*pmd), pmd_dirty(*pmd),
+		      locked, migration);
 }
 #else
 static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
@@ -1378,6 +1396,7 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
 {
 	u64 frame = 0, flags = 0;
 	struct page *page = NULL;
+	bool migration = false;
 
 	if (pte_present(pte)) {
 		if (pm->show_pfn)
@@ -1399,13 +1418,14 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
 			frame = swp_type(entry) |
 				(swp_offset(entry) << MAX_SWAPFILES_SHIFT);
 		flags |= PM_SWAP;
+		migration = is_migration_entry(entry);
 		if (is_pfn_swap_entry(entry))
 			page = pfn_swap_entry_to_page(entry);
 	}
 
 	if (page && !PageAnon(page))
 		flags |= PM_FILE;
-	if (page && page_mapcount(page) == 1)
+	if (page && !migration && page_mapcount(page) == 1)
 		flags |= PM_MMAP_EXCLUSIVE;
 	if (vma->vm_flags & VM_SOFTDIRTY)
 		flags |= PM_SOFT_DIRTY;
@@ -1421,8 +1441,9 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
 	spinlock_t *ptl;
 	pte_t *pte, *orig_pte;
 	int err = 0;
-
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	bool migration = false;
+
 	ptl = pmd_trans_huge_lock(pmdp, vma);
 	if (ptl) {
 		u64 flags = 0, frame = 0;
@@ -1461,11 +1482,12 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
 			if (pmd_swp_uffd_wp(pmd))
 				flags |= PM_UFFD_WP;
 			VM_BUG_ON(!is_pmd_migration_entry(pmd));
+			migration = is_migration_entry(entry);
 			page = pfn_swap_entry_to_page(entry);
 		}
 #endif
 
-		if (page && page_mapcount(page) == 1)
+		if (page && !migration && page_mapcount(page) == 1)
 			flags |= PM_MMAP_EXCLUSIVE;
 
 		for (; addr != end; addr += PAGE_SIZE) {