From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: 2.6.35-rc2-git1 - include/linux/cgroup.h:534 invoked rcu_dereference_check() without protection! Date: Tue, 08 Jun 2010 10:40:41 +0200 Message-ID: <1275986441.5408.111.camel@twins> References: <20100608001929.GF2387@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Cc: paulmck@linux.vnet.ibm.com, Vivek Goyal , Eric Paris , Lai Jiangshan , Ingo Molnar , LKML , nauman@google.com, eric.dumazet@gmail.com, netdev@vger.kernel.org, Jens Axboe , Gui Jianfeng , Li Zefan , Johannes Berg To: Miles Lane Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, 2010-06-08 at 00:16 -0400, Miles Lane wrote: > On Mon, Jun 7, 2010 at 8:19 PM, Paul E. McKenney > wrote: > > On Mon, Jun 07, 2010 at 02:14:25PM -0400, Miles Lane wrote: > >> Hi All, > >> > >> I just reproduced a warning I reported quite a while ago. Is a patch > >> for this in the pipeline? > > > > I proposed a patch, thinking that it was a false positive. Peter Zijlstra > > pointed out that there was a real race, and proposed an alternative patch, > > which may be found at http://lkml.org/lkml/2010/4/22/603. > > > > Could you please test Peter's patch and let us know if it cures the problem? > > Gah, this task_group() stuff is annoying, how about something like the below which teaches task_group() about the task_rq()->lock rule? --- include/linux/cgroup.h | 20 +++++++++++---- kernel/sched.c | 61 +++++++++++++++++++++++++---------------------- 2 files changed, 46 insertions(+), 35 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 0c62160..1efd212 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -525,13 +525,21 @@ static inline struct cgroup_subsys_state *cgroup_subsys_state( return cgrp->subsys[subsys_id]; } -static inline struct cgroup_subsys_state *task_subsys_state( - struct task_struct *task, int subsys_id) +/* + * function to get the cgroup_subsys_state which allows for extra + * rcu_dereference_check() conditions, such as locks used during the + * cgroup_subsys::attach() methods. + */ +#define task_subsys_state_check(task, subsys_id, __c) \ + rcu_dereference_check(task->cgroups->subsys[subsys_id], \ + rcu_read_lock_held() || \ + lockdep_is_held(&task->alloc_lock) || \ + cgroup_lock_is_held() || (__c)) + +static inline struct cgroup_subsys_state * +task_subsys_state(struct task_struct *task, int subsys_id) { - return rcu_dereference_check(task->cgroups->subsys[subsys_id], - rcu_read_lock_held() || - lockdep_is_held(&task->alloc_lock) || - cgroup_lock_is_held()); + return task_subsys_state_check(task, subsys_id, false); } static inline struct cgroup* task_cgroup(struct task_struct *task, diff --git a/kernel/sched.c b/kernel/sched.c index f8b8996..e01bb45 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -306,32 +306,26 @@ static int init_task_group_load = INIT_TASK_GROUP_LOAD; */ struct task_group init_task_group; -/* return group to which a task belongs */ +/* + * Return the group to which this tasks belongs. + * + * We use task_subsys_state_check() and extend the RCU verification + * with lockdep_is_held(&task_rq(p)->lock) because cpu_cgroup_attach() + * holds that lock for each task it moves into the cgroup. Therefore + * by holding that lock, we pin the task to the current cgroup. + */ static inline struct task_group *task_group(struct task_struct *p) { - struct task_group *tg; + struct cgroup_subsys_state *css; -#ifdef CONFIG_CGROUP_SCHED - tg = container_of(task_subsys_state(p, cpu_cgroup_subsys_id), - struct task_group, css); -#else - tg = &init_task_group; -#endif - return tg; + css = task_subsys_state_check(p, cpu_cgroup_subsys_id, + lockdep_is_held(&task_rq(p)->lock)); + return container_of(css, struct task_group, css); } /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */ static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { - /* - * Strictly speaking this rcu_read_lock() is not needed since the - * task_group is tied to the cgroup, which in turn can never go away - * as long as there are tasks attached to it. - * - * However since task_group() uses task_subsys_state() which is an - * rcu_dereference() user, this quiets CONFIG_PROVE_RCU. - */ - rcu_read_lock(); #ifdef CONFIG_FAIR_GROUP_SCHED p->se.cfs_rq = task_group(p)->cfs_rq[cpu]; p->se.parent = task_group(p)->se[cpu]; @@ -341,7 +335,6 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu) p->rt.rt_rq = task_group(p)->rt_rq[cpu]; p->rt.parent = task_group(p)->rt_se[cpu]; #endif - rcu_read_unlock(); } #else @@ -4465,16 +4458,6 @@ recheck: } if (user) { -#ifdef CONFIG_RT_GROUP_SCHED - /* - * Do not allow realtime tasks into groups that have no runtime - * assigned. - */ - if (rt_bandwidth_enabled() && rt_policy(policy) && - task_group(p)->rt_bandwidth.rt_runtime == 0) - return -EPERM; -#endif - retval = security_task_setscheduler(p, policy, param); if (retval) return retval; @@ -4490,6 +4473,26 @@ recheck: * runqueue lock must be held. */ rq = __task_rq_lock(p); + + retval = 0; +#ifdef CONFIG_RT_GROUP_SCHED + if (user) { + /* + * Do not allow realtime tasks into groups that have no runtime + * assigned. + */ + if (rt_bandwidth_enabled() && rt_policy(policy) && + task_group(p)->rt_bandwidth.rt_runtime == 0) + retval = -EPERM; + + if (retval) { + __task_rq_unlock(rq); + raw_spin_unlock_irqrestore(&p->pi_lock, flags); + return retval; + } + } +#endif + /* recheck policy now with rq lock held */ if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) { policy = oldpolicy = -1;