From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752555Ab1DOSjN (ORCPT ); Fri, 15 Apr 2011 14:39:13 -0400 Received: from mga09.intel.com ([134.134.136.24]:44674 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752069Ab1DOSjM (ORCPT ); Fri, 15 Apr 2011 14:39:12 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.64,220,1301900400"; d="scan'208";a="733978339" Subject: [PATCH] vfs: Fix RCU path walk failiures due to uninitialized nameidata seq number for root directory From: Tim Chen To: Alexander Viro , Nick Piggin Cc: Andi Kleen , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, shaohua.li@intel.com, alex.shi@intel.com Content-Type: text/plain; charset="UTF-8" Date: Fri, 15 Apr 2011 11:39:29 -0700 Message-ID: <1302892769.2577.24.camel@schen9-DESK> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 (2.28.3-1.fc12) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org During RCU walk in path_lookupat and path_openat, the rcu lookup frequently failed because when root directory was looked up, seq number was not properly set in nameidata. We dropped out of RCU walk in nameidata_drop_rcu due to mismatch in directory entry's seq number. We reverted to slow path walk that need to take references. With the following patch, I saw a 50% increase in an exim mail server benchmark throughput on a 4-socket Nehalem-EX system. Thanks. Tim Signed-off-by: Tim Chen diff --git a/fs/namei.c b/fs/namei.c index 3cb616d..e4b27a6 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -697,6 +697,7 @@ static __always_inline void set_root_rcu(struct nameidata *nd) do { seq = read_seqcount_begin(&fs->seq); nd->root = fs->root; + nd->seq = __read_seqcount_begin(&nd->root.dentry->d_seq); } while (read_seqcount_retry(&fs->seq, seq)); } }