[PATCH v7 2/2] mm: fix the handling Non-LRU pages returned by follow_page

[Haiyue Wang]

The handling Non-LRU pages returned by follow_page() jumps directly, it
doesn't call put_page() to handle the reference count, since 'FOLL_GET'
flag for follow_page() has get_page() called. Fix the zone device page
check by handling the page reference count correctly before returning.

And as David reviewed, "device pages are never PageKsm pages". Drop this
zone device page check for break_ksm().

Since the zone device page can't be a transparent huge page, so drop the
redundant zone device page check for split_huge_pages_pid(). (by Miaohe)

Fixes: 3218f8712d6b ("mm: handling Non-LRU pages returned by vm_normal_pages")
Signed-off-by: Haiyue Wang <haiyue.wang@xxxxxxxxx>
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Reviewed-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
---
 mm/huge_memory.c |  2 +-
 mm/ksm.c         | 12 +++++++++---
 mm/migrate.c     | 19 ++++++++++++-------
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8a7c1b344abe..2ee6d38a1426 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2963,7 +2963,7 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
 		/* FOLL_DUMP to ignore special (like zero) pages */
 		page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
 
-		if (IS_ERR_OR_NULL(page) || is_zone_device_page(page))
+		if (IS_ERR_OR_NULL(page))
 			continue;
 
 		if (!is_transparent_hugepage(page))
diff --git a/mm/ksm.c b/mm/ksm.c
index 42ab153335a2..e26f57fc1f0e 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -475,7 +475,7 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 		cond_resched();
 		page = follow_page(vma, addr,
 				FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
-		if (IS_ERR_OR_NULL(page) || is_zone_device_page(page))
+		if (IS_ERR_OR_NULL(page))
 			break;
 		if (PageKsm(page))
 			ret = handle_mm_fault(vma, addr,
@@ -560,12 +560,15 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 		goto out;
 
 	page = follow_page(vma, addr, FOLL_GET);
-	if (IS_ERR_OR_NULL(page) || is_zone_device_page(page))
+	if (IS_ERR_OR_NULL(page))
 		goto out;
+	if (is_zone_device_page(page))
+		goto out_putpage;
 	if (PageAnon(page)) {
 		flush_anon_page(vma, page, addr);
 		flush_dcache_page(page);
 	} else {
+out_putpage:
 		put_page(page);
 out:
 		page = NULL;
@@ -2308,11 +2311,13 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
 			if (ksm_test_exit(mm))
 				break;
 			*page = follow_page(vma, ksm_scan.address, FOLL_GET);
-			if (IS_ERR_OR_NULL(*page) || is_zone_device_page(*page)) {
+			if (IS_ERR_OR_NULL(*page)) {
 				ksm_scan.address += PAGE_SIZE;
 				cond_resched();
 				continue;
 			}
+			if (is_zone_device_page(*page))
+				goto next_page;
 			if (PageAnon(*page)) {
 				flush_anon_page(vma, *page, ksm_scan.address);
 				flush_dcache_page(*page);
@@ -2327,6 +2332,7 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
 				mmap_read_unlock(mm);
 				return rmap_item;
 			}
+next_page:
 			put_page(*page);
 			ksm_scan.address += PAGE_SIZE;
 			cond_resched();
diff --git a/mm/migrate.c b/mm/migrate.c
index 581dfaad9257..44e05ce41d49 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1672,9 +1672,12 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
 		goto out;
 
 	err = -ENOENT;
-	if (!page || is_zone_device_page(page))
+	if (!page)
 		goto out;
 
+	if (is_zone_device_page(page))
+		goto out_putpage;
+
 	err = 0;
 	if (page_to_nid(page) == node)
 		goto out_putpage;
@@ -1868,13 +1871,15 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
 		if (IS_ERR(page))
 			goto set_status;
 
-		if (page && !is_zone_device_page(page)) {
+		err = -ENOENT;
+		if (!page)
+			goto set_status;
+
+		if (!is_zone_device_page(page))
 			err = page_to_nid(page);
-			if (foll_flags & FOLL_GET)
-				put_page(page);
-		} else {
-			err = -ENOENT;
-		}
+
+		if (foll_flags & FOLL_GET)
+			put_page(page);
 set_status:
 		*status = err;
 
-- 
2.37.2