Separate out THP logic so we can drop an indentation level and reduce the
amount of noise in this function.

We add pagemap_pmd_range_thp() for this purpose.

While we're here, convert the VM_BUG_ON() to a VM_WARN_ON_ONCE() at the
same time.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 fs/proc/task_mmu.c | 146 +++++++++++++++++++++++----------------------
 1 file changed, 76 insertions(+), 70 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 5475acfa1a33..3c8be2579253 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1984,91 +1984,97 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
 	return make_pme(frame, flags);
 }
 
-static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
-			     struct mm_walk *walk)
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned long addr,
+		unsigned long end, struct vm_area_struct *vma,
+		struct pagemapread *pm, spinlock_t *ptl)
 {
-	struct vm_area_struct *vma = walk->vma;
-	struct pagemapread *pm = walk->private;
-	spinlock_t *ptl;
-	pte_t *pte, *orig_pte;
+	unsigned int idx = (addr & ~PMD_MASK) >> PAGE_SHIFT;
+	u64 flags = 0, frame = 0;
+	pmd_t pmd = *pmdp;
+	struct page *page = NULL;
+	struct folio *folio = NULL;
 	int err = 0;
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 
-	ptl = pmd_trans_huge_lock(pmdp, vma);
-	if (ptl) {
-		unsigned int idx = (addr & ~PMD_MASK) >> PAGE_SHIFT;
-		u64 flags = 0, frame = 0;
-		pmd_t pmd = *pmdp;
-		struct page *page = NULL;
-		struct folio *folio = NULL;
+	if (vma->vm_flags & VM_SOFTDIRTY)
+		flags |= PM_SOFT_DIRTY;
 
-		if (vma->vm_flags & VM_SOFTDIRTY)
-			flags |= PM_SOFT_DIRTY;
+	if (pmd_present(pmd)) {
+		page = pmd_page(pmd);
 
-		if (pmd_present(pmd)) {
-			page = pmd_page(pmd);
+		flags |= PM_PRESENT;
+		if (pmd_soft_dirty(pmd))
+			flags |= PM_SOFT_DIRTY;
+		if (pmd_uffd_wp(pmd))
+			flags |= PM_UFFD_WP;
+		if (pm->show_pfn)
+			frame = pmd_pfn(pmd) + idx;
+	} else if (thp_migration_supported() && is_swap_pmd(pmd)) {
+		swp_entry_t entry = pmd_to_swp_entry(pmd);
+		unsigned long offset;
 
-			flags |= PM_PRESENT;
-			if (pmd_soft_dirty(pmd))
-				flags |= PM_SOFT_DIRTY;
-			if (pmd_uffd_wp(pmd))
-				flags |= PM_UFFD_WP;
-			if (pm->show_pfn)
-				frame = pmd_pfn(pmd) + idx;
-		}
-#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
-		else if (is_swap_pmd(pmd)) {
-			swp_entry_t entry = pmd_to_swp_entry(pmd);
-			unsigned long offset;
-
-			if (pm->show_pfn) {
-				if (is_pfn_swap_entry(entry))
-					offset = swp_offset_pfn(entry) + idx;
-				else
-					offset = swp_offset(entry) + idx;
-				frame = swp_type(entry) |
-					(offset << MAX_SWAPFILES_SHIFT);
-			}
-			flags |= PM_SWAP;
-			if (pmd_swp_soft_dirty(pmd))
-				flags |= PM_SOFT_DIRTY;
-			if (pmd_swp_uffd_wp(pmd))
-				flags |= PM_UFFD_WP;
-			VM_BUG_ON(!is_pmd_migration_entry(pmd));
-			page = pfn_swap_entry_to_page(entry);
+		if (pm->show_pfn) {
+			if (is_pfn_swap_entry(entry))
+				offset = swp_offset_pfn(entry) + idx;
+			else
+				offset = swp_offset(entry) + idx;
+			frame = swp_type(entry) |
+				(offset << MAX_SWAPFILES_SHIFT);
 		}
-#endif
+		flags |= PM_SWAP;
+		if (pmd_swp_soft_dirty(pmd))
+			flags |= PM_SOFT_DIRTY;
+		if (pmd_swp_uffd_wp(pmd))
+			flags |= PM_UFFD_WP;
+		VM_WARN_ON_ONCE(!is_pmd_migration_entry(pmd));
+		page = pfn_swap_entry_to_page(entry);
+	}
 
-		if (page) {
-			folio = page_folio(page);
-			if (!folio_test_anon(folio))
-				flags |= PM_FILE;
-		}
+	if (page) {
+		folio = page_folio(page);
+		if (!folio_test_anon(folio))
+			flags |= PM_FILE;
+	}
 
-		for (; addr != end; addr += PAGE_SIZE, idx++) {
-			u64 cur_flags = flags;
-			pagemap_entry_t pme;
+	for (; addr != end; addr += PAGE_SIZE, idx++) {
+		u64 cur_flags = flags;
+		pagemap_entry_t pme;
 
-			if (folio && (flags & PM_PRESENT) &&
-			    __folio_page_mapped_exclusively(folio, page))
-				cur_flags |= PM_MMAP_EXCLUSIVE;
+		if (folio && (flags & PM_PRESENT) &&
+		    __folio_page_mapped_exclusively(folio, page))
+			cur_flags |= PM_MMAP_EXCLUSIVE;
 
-			pme = make_pme(frame, cur_flags);
-			err = add_to_pagemap(&pme, pm);
-			if (err)
-				break;
-			if (pm->show_pfn) {
-				if (flags & PM_PRESENT)
-					frame++;
-				else if (flags & PM_SWAP)
-					frame += (1 << MAX_SWAPFILES_SHIFT);
-			}
+		pme = make_pme(frame, cur_flags);
+		err = add_to_pagemap(&pme, pm);
+		if (err)
+			break;
+		if (pm->show_pfn) {
+			if (flags & PM_PRESENT)
+				frame++;
+			else if (flags & PM_SWAP)
+				frame += (1 << MAX_SWAPFILES_SHIFT);
 		}
-		spin_unlock(ptl);
-		return err;
 	}
+	spin_unlock(ptl);
+	return err;
+}
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
+static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
+			     struct mm_walk *walk)
+{
+	struct vm_area_struct *vma = walk->vma;
+	struct pagemapread *pm = walk->private;
+	spinlock_t *ptl;
+	pte_t *pte, *orig_pte;
+	int err = 0;
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	ptl = pmd_trans_huge_lock(pmdp, vma);
+	if (ptl)
+		return pagemap_pmd_range_thp(pmdp, addr, end, vma, pm, ptl);
+#endif
+
 	/*
 	 * We can assume that @vma always points to a valid one and @end never
 	 * goes beyond vma->vm_end.
-- 
2.51.0