From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: [patch 24/28] fs: dcache reduce d_parent locking Date: Wed, 17 Nov 2010 01:09:24 +1100 Message-ID: <20101116142030.517382183@kernel.dk> References: <20101116140900.039761100@kernel.dk> Cc: linux-kernel@vger.kernel.org To: linux-fsdevel@vger.kernel.org Return-path: Received: from ipmail05.adl6.internode.on.net ([150.101.137.143]:32788 "EHLO ipmail05.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758625Ab0KPOX7 (ORCPT ); Tue, 16 Nov 2010 09:23:59 -0500 Content-Disposition: inline; filename=fs-dget_parent-opt.patch Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Use RCU to simplify locking in dget_parent. Signed-off-by: Nick Piggin --- fs/dcache.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) Index: linux-2.6/fs/dcache.c =================================================================== --- linux-2.6.orig/fs/dcache.c 2010-11-17 00:52:38.000000000 +1100 +++ linux-2.6/fs/dcache.c 2010-11-17 01:05:38.000000000 +1100 @@ -406,24 +406,27 @@ struct dentry *dget_parent(struct dentry struct dentry *ret; repeat: - spin_lock(&dentry->d_lock); + /* + * Don't need rcu_dereference because we re-check it was correct under + * the lock. + */ + rcu_read_lock(); ret = dentry->d_parent; - if (!ret) - goto out; - if (dentry == ret) { - ret->d_count++; - goto out; - } - if (!spin_trylock(&ret->d_lock)) { - spin_unlock(&dentry->d_lock); - cpu_relax(); + if (!ret) { + rcu_read_unlock(); + goto out; + } + spin_lock(&ret->d_lock); + if (unlikely(ret != dentry->d_parent)) { + spin_unlock(&ret->d_lock); + rcu_read_unlock(); goto repeat; } + rcu_read_unlock(); BUG_ON(!ret->d_count); ret->d_count++; spin_unlock(&ret->d_lock); out: - spin_unlock(&dentry->d_lock); return ret; } EXPORT_SYMBOL(dget_parent);