Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757663Ab0DVTzo (ORCPT ); Thu, 22 Apr 2010 15:55:44 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:38511 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756656Ab0DVTzj (ORCPT ); Thu, 22 Apr 2010 15:55:39 -0400 Date: Thu, 22 Apr 2010 12:55:33 -0700 From: "Paul E. McKenney" To: Li Zefan Cc: LKML , "containers@lists.osdl.org" , Paul Menage , Andrew Morton Subject: Re: [PATCH 1/5] cgroup: Fix an RCU warning in cgroup_path() Message-ID: <20100422195533.GI2524@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <4BD016F4.8060108@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BD016F4.8060108@cn.fujitsu.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2036 Lines: 65 On Thu, Apr 22, 2010 at 05:29:24PM +0800, Li Zefan wrote: > with CONFIG_PROVE_RCU=y, a warning can be triggered: > > # mount -t cgroup -o debug xxx /mnt > # cat /proc/$$/cgroup > > ... > kernel/cgroup.c:1649 invoked rcu_dereference_check() without protection! > ... > > This is a false-positive, because cgroup_path() can be called > with either rcu_read_lock() held or cgroup_mutex held. Queued for 2.6.34, thank you Li! Thanx, Paul > Signed-off-by: Li Zefan > --- > kernel/cgroup.c | 12 +++++++++--- > 1 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index e2769e1..4ca928d 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -1646,7 +1646,9 @@ static inline struct cftype *__d_cft(struct dentry *dentry) > int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen) > { > char *start; > - struct dentry *dentry = rcu_dereference(cgrp->dentry); > + struct dentry *dentry = rcu_dereference_check(cgrp->dentry, > + rcu_read_lock_held() || > + cgroup_lock_is_held()); > > if (!dentry || cgrp == dummytop) { > /* > @@ -1662,13 +1664,17 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen) > *--start = '\0'; > for (;;) { > int len = dentry->d_name.len; > + > if ((start -= len) < buf) > return -ENAMETOOLONG; > - memcpy(start, cgrp->dentry->d_name.name, len); > + memcpy(start, dentry->d_name.name, len); > cgrp = cgrp->parent; > if (!cgrp) > break; > - dentry = rcu_dereference(cgrp->dentry); > + > + dentry = rcu_dereference_check(cgrp->dentry, > + rcu_read_lock_held() || > + cgroup_lock_is_held()); > if (!cgrp->parent) > continue; > if (--start < buf) > -- > 1.6.3 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/