NFS: Try to commit unstable writes in nfs_release_page()

If someone calls nfs_release_page(), we presumably already know that the
page is clean, however it may be holding an unstable write.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfs/file.c

@@ -486,6 +486,8 @@ static int nfs_release_page(struct page *page, gfp_t gfp)
 {
 	dfprintk(PAGECACHE, "NFS: release_page(%p)\n", page);
 
+	if (gfp & __GFP_WAIT)
+		nfs_wb_page(page->mapping->host, page);
 	/* If PagePrivate() is set, then the page is not freeable */
 	if (PagePrivate(page))
 		return 0;