f2fs: fix to add refcount once page is tagged PG_private

As Gao Xiang reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=202749

f2fs may skip pageout() due to incorrect page reference count.

The problem here is that MM defined the rule [1] very clearly that
once page was set with PG_private flag, we should increment the
refcount in that page, also main flows like pageout(), migrate_page()
will assume there is one additional page reference count if
page_has_private() returns true.

But currently, f2fs won't add/del refcount when changing PG_private
flag. Anyway, f2fs should follow MM's rule to make MM's related flows
running as expected.

[1] https://lore.kernel.org/lkml/[e-mail]/

Reported-by: Gao Xiang <[e-mail]>
Signed-off-by: Chao Yu <[e-mail]>
Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/checkpoint.c

···
 	if (!PageDirty(page)) {
 		__set_page_dirty_nobuffers(page);
 		inc_page_count(F2FS_P_SB(page), F2FS_DIRTY_META);
-		SetPagePrivate(page);
+		f2fs_set_page_private(page, 0);
 		f2fs_trace_pid(page);
 		return 1;
 	}
···
 	inode_inc_dirty_pages(inode);
 	spin_unlock(&sbi->inode_lock[type]);
 
-	SetPagePrivate(page);
+	f2fs_set_page_private(page, 0);
 	f2fs_trace_pid(page);
 }
 

fs/f2fs/data.c

···
 	if (IS_ATOMIC_WRITTEN_PAGE(page))
 		return f2fs_drop_inmem_page(inode, page);
 
-	set_page_private(page, 0);
-	ClearPagePrivate(page);
+	f2fs_clear_page_private(page);
 }
 
 int f2fs_release_page(struct page *page, gfp_t wait)
···
 		return 0;
 
 	clear_cold_data(page);
-	set_page_private(page, 0);
-	ClearPagePrivate(page);
+	f2fs_clear_page_private(page);
 	return 1;
 }
 
···
 			return -EAGAIN;
 	}
 
-	/*
-	 * A reference is expected if PagePrivate set when move mapping,
-	 * however F2FS breaks this for maintaining dirty page counts when
-	 * truncating pages. So here adjusting the 'extra_count' make it work.
-	 */
-	extra_count = (atomic_written ? 1 : 0) - page_has_private(page);
+	/* one extra reference was held for atomic_write page */
+	extra_count = atomic_written ? 1 : 0;
 	rc = migrate_page_move_mapping(mapping, newpage,
 				page, mode, extra_count);
 	if (rc != MIGRATEPAGE_SUCCESS) {
···
 		get_page(newpage);
 	}
 
-	if (PagePrivate(page))
-		SetPagePrivate(newpage);
-	set_page_private(newpage, page_private(page));
+	if (PagePrivate(page)) {
+		f2fs_set_page_private(newpage, page_private(page));
+		f2fs_clear_page_private(page);
+	}
 
 	if (mode != MIGRATE_SYNC_NO_COPY)
 		migrate_page_copy(newpage, page);

fs/f2fs/dir.c

···
 		!f2fs_truncate_hole(dir, page->index, page->index + 1)) {
 		f2fs_clear_page_cache_dirty_tag(page);
 		clear_page_dirty_for_io(page);
-		ClearPagePrivate(page);
+		f2fs_clear_page_private(page);
 		ClearPageUptodate(page);
 		clear_cold_data(page);
 		inode_dec_dirty_pages(dir);

fs/f2fs/f2fs.h

···
 	return true;
 }
 
+static inline void f2fs_set_page_private(struct page *page,
+						unsigned long data)
+{
+	if (PagePrivate(page))
+		return;
+
+	get_page(page);
+	SetPagePrivate(page);
+	set_page_private(page, data);
+}
+
+static inline void f2fs_clear_page_private(struct page *page)
+{
+	if (!PagePrivate(page))
+		return;
+
+	set_page_private(page, 0);
+	ClearPagePrivate(page);
+	f2fs_put_page(page, 0);
+}
+
 /*
  * file.c
  */

fs/f2fs/node.c

···
 	if (!PageDirty(page)) {
 		__set_page_dirty_nobuffers(page);
 		inc_page_count(F2FS_P_SB(page), F2FS_DIRTY_NODES);
-		SetPagePrivate(page);
+		f2fs_set_page_private(page, 0);
 		f2fs_trace_pid(page);
 		return 1;
 	}

fs/f2fs/segment.c

···
 
 	f2fs_trace_pid(page);
 
-	set_page_private(page, (unsigned long)ATOMIC_WRITTEN_PAGE);
-	SetPagePrivate(page);
+	f2fs_set_page_private(page, (unsigned long)ATOMIC_WRITTEN_PAGE);
 
 	new = f2fs_kmem_cache_alloc(inmem_entry_slab, GFP_NOFS);
 
···
 			ClearPageUptodate(page);
 			clear_cold_data(page);
 		}
-		set_page_private(page, 0);
-		ClearPagePrivate(page);
+		f2fs_clear_page_private(page);
 		f2fs_put_page(page, 1);
 
 		list_del(&cur->list);
···
 	kmem_cache_free(inmem_entry_slab, cur);
 
 	ClearPageUptodate(page);
-	set_page_private(page, 0);
-	ClearPagePrivate(page);
+	f2fs_clear_page_private(page);
 	f2fs_put_page(page, 0);
 
 	trace_f2fs_commit_inmem_page(page, INMEM_INVALIDATE);