NFSv42: Fix pagecache invalidation after COPY/CLONE

The mechanism in use to allow the client to see the results of COPY/CLONE
is to drop those pages from the pagecache.  This forces the client to read
those pages once more from the server.  However, truncate_pagecache_range()
zeros out partial pages instead of dropping them.  Let us instead use
invalidate_inode_pages2_range() with full-page offsets to ensure the client
properly sees the results of COPY/CLONE operations.

Cc: <stable@vger.kernel.org> # v4.7+
Fixes: 2e72448b07 ("NFS: Add COPY nfs operation")
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs42proc.c

@@ -289,7 +289,9 @@ static void nfs42_copy_dest_done(struct inode *inode, loff_t pos, loff_t len)
 	loff_t newsize = pos + len;
 	loff_t end = newsize - 1;
 
-	truncate_pagecache_range(inode, pos, end);
+	WARN_ON_ONCE(invalidate_inode_pages2_range(inode->i_mapping,
+				pos >> PAGE_SHIFT, end >> PAGE_SHIFT));
+
 	spin_lock(&inode->i_lock);
 	if (newsize > i_size_read(inode))
 		i_size_write(inode, newsize);