[PATCH] v9fs: fix fd_close

If a 9pfs server crashes, v9fs_fd_close() is called.  Subsequently, in
cleaning up by performing a umount() on the FS that was provided by this
server v9fs_fd_close() is called again, and uses the old, freed valus of
trans->priv.  This patch ensures that trans->priv can be freed only once,
otherwise this function bails early.
Signed-off-by: NMichal Ostrowski <mostrows@watson.ibm.com>
Signed-off-by: NEric Van Hensbergen <ericvh@gmail.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/9p/trans_fd.c

@@ -148,12 +148,12 @@ static void v9fs_fd_close(struct v9fs_transport *trans)
 	if (!trans)
 		return;
 
-	trans->status = Disconnected;
-	ts = trans->priv;
+	ts = xchg(&trans->priv, NULL);
 
 	if (!ts)
 		return;
 
+	trans->status = Disconnected;
 	if (ts->in_file)
 		fput(ts->in_file);