afs: Avoid endless loop if file is larger than expected

afs_read_dir fetches an amount of data that's based on what the inode
size is thought to be.  If the file on the server is larger than what
was fetched, the code rechecks i_size and retries.  If the local i_size
was not properly updated, this can lead to an endless loop of fetching
i_size from the server and noticing each time that the size is larger on
the server.

If it is known that the remote size is larger than i_size, bump up the
fetch size to that size.

Fixes: f3ddee8 ("afs: Fix directory handling")
Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-afs@lists.infradead.org

Author: Marc Dionne

fs/afs/dir.c

@@ -275,6 +275,7 @@ static struct afs_read *afs_read_dir(struct afs_vnode *dvnode, struct key *key)
 	loff_t i_size;
 	int nr_pages, i;
 	int ret;
+	loff_t remote_size = 0;
 
 	_enter("");
 
@@ -289,6 +290,8 @@ static struct afs_read *afs_read_dir(struct afs_vnode *dvnode, struct key *key)
 
 expand:
 	i_size = i_size_read(&dvnode->netfs.inode);
+	if (i_size < remote_size)
+	    i_size = remote_size;
 	if (i_size < 2048) {
 		ret = afs_bad(dvnode, afs_file_error_dir_small);
 		goto error;
@@ -364,6 +367,7 @@ static struct afs_read *afs_read_dir(struct afs_vnode *dvnode, struct key *key)
 			 * buffer.
 			 */
 			up_write(&dvnode->validate_lock);
+			remote_size = req->file_size;
 			goto expand;
 		}