[PATCH] ubifs: Get/put page when changing PG_private

[Richard Weinberger]

The page migration code assumes that a page with PG_private
set has its page count elevated by 1.
UBIFS never did this and therefore the migration code was unable
to migrate some pages owned by UBIFS.
The lead to situations where the CMA memory allocator failed to
allocate memory.

Fix this by using get/put_page when changing PG_private.

Cc: <stable@xxxxxxxxxxxxxxx>
Cc: zhangjun <openzhangj@xxxxxxxxx>
Fixes: 4ac1c17b2044 ("UBIFS: Implement ->migratepage()")
Reported-by: zhangjun <openzhangj@xxxxxxxxx>
Signed-off-by: Richard Weinberger <richard@xxxxxx>
---
zhangjun,

Please give this patch a try!

Thanks,
//richard
---
 fs/ubifs/file.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 1b78f2e09218..abe940d0767c 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -582,6 +582,7 @@ static int ubifs_write_end(struct file *file, struct address_space *mapping,
 	}
 
 	if (!PagePrivate(page)) {
+		get_page(page);
 		SetPagePrivate(page);
 		atomic_long_inc(&c->dirty_pg_cnt);
 		__set_page_dirty_nobuffers(page);
@@ -959,6 +960,7 @@ static int do_writepage(struct page *page, int len)
 	atomic_long_dec(&c->dirty_pg_cnt);
 	ClearPagePrivate(page);
 	ClearPageChecked(page);
+	put_page(page);
 
 	kunmap(page);
 	unlock_page(page);
@@ -1318,6 +1320,7 @@ static void ubifs_invalidatepage(struct page *page, unsigned int offset,
 	atomic_long_dec(&c->dirty_pg_cnt);
 	ClearPagePrivate(page);
 	ClearPageChecked(page);
+	put_page(page);
 }
 
 int ubifs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
@@ -1487,6 +1490,8 @@ static int ubifs_migrate_page(struct address_space *mapping,
 
 	if (PagePrivate(page)) {
 		ClearPagePrivate(page);
+		put_page(page);
+		get_page(newpage);
 		SetPagePrivate(newpage);
 	}
 
@@ -1513,6 +1518,7 @@ static int ubifs_releasepage(struct page *page, gfp_t unused_gfp_flags)
 	ubifs_assert(c, 0);
 	ClearPagePrivate(page);
 	ClearPageChecked(page);
+	put_page(page);
 	return 1;
 }
 
@@ -1582,6 +1588,7 @@ static vm_fault_t ubifs_vm_page_mkwrite(struct vm_fault *vmf)
 	else {
 		if (!PageChecked(page))
 			ubifs_convert_page_budget(c);
+		get_page(page);
 		SetPagePrivate(page);
 		atomic_long_inc(&c->dirty_pg_cnt);
 		__set_page_dirty_nobuffers(page);
-- 
2.20.0