fs: ramfs: file-nommu: add SetPageUptodate()

There is a bug in the below scenario for !CONFIG_MMU:

 1. create a new file
 2. mmap the file and write to it
 3. read the file can't get the correct value

Because

  sys_read() -> generic_file_aio_read() -> simple_readpage() -> clear_page()

which causes the page to be zeroed.

Add SetPageUptodate() to ramfs_nommu_expand_for_mapping() so that
generic_file_aio_read() do not call simple_readpage().

Signed-off-by: Bob Liu <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: David Howells <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Greg Ungerer <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/ramfs/file-nommu.c

@@ -110,6 +110,7 @@ int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
 
 		/* prevent the page from being discarded on memory pressure */
 		SetPageDirty(page);
+		SetPageUptodate(page);
 
 		unlock_page(page);
 		put_page(page);