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/2b19b3c4-2bc4-15fa-15cc-27a13e5c7af1@aol.com/

Reported-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 3007759dd2dd..a165f7870004 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2835,6 +2835,27 @@ static inline bool is_valid_data_blkaddr(struct f2fs_sb_info *sbi,
 	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
  */