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Date: Wed, 9 Jun 2010 11:11:44 -0400
From: Miles Lane <miles.lane@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: paulmck@...ux.vnet.ibm.com, Vivek Goyal <vgoyal@...hat.com>,
Eric Paris <eparis@...hat.com>,
Lai Jiangshan <laijs@...fujitsu.com>,
Ingo Molnar <mingo@...e.hu>,
LKML <linux-kernel@...r.kernel.org>, nauman@...gle.com,
eric.dumazet@...il.com, netdev@...r.kernel.org,
Jens Axboe <jens.axboe@...cle.com>,
Gui Jianfeng <guijianfeng@...fujitsu.com>,
Li Zefan <lizf@...fujitsu.com>,
Johannes Berg <johannes@...solutions.net>
Subject: Re: 2.6.35-rc2-git1 - include/linux/cgroup.h:534 invoked
rcu_dereference_check() without protection!
On Tue, Jun 8, 2010 at 9:34 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2010-06-08 at 09:14 -0400, Miles Lane wrote:
>
>> CC kernel/sched.o
>> kernel/sched.c: In function ‘task_group’:
>> kernel/sched.c:321: error: implicit declaration of function ‘task_rq’
>> kernel/sched.c:321: error: invalid type argument of ‘->’ (have ‘int’)
>> make[1]: *** [kernel/sched.o] Error 1
>>
>> I had to apply with fuzz. Did it mess up?
>
>
> No, I probably did.. task_rq() is defined on line 636 or thereabouts,
> and this function landed around line 320.
>
> Ahh, and it compiled here because I have CGROUP_SCHED=y, but
> PROVE_RCU=n, so that whole check expression disappears and is never
> evaluated...
>
> /me fixes
>
> ---
> Subject: sched: PROVE_RCU vs cpu_cgroup
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Tue Jun 08 11:40:42 CEST 2010
>
> PROVE_RCU has a few issues with the cpu_cgroup because the scheduler
> typically holds rq->lock around the css rcu derefs but the generic
> cgroup code doesn't (and can't) know about that lock.
>
> Provide means to add extra checks to the css dereference and use that
> in the scheduler to annotate its users.
>
> The addition of rq->lock to these checks is correct because the
> cgroup_subsys::attach() method takes the rq->lock for each task it
> moves, therefore by holding that lock, we ensure the task is pinned to
> the current cgroup and the RCU dereference is valid.
>
> That leaves one genuine race in __sched_setscheduler() where we used
> task_group() without holding any of the required locks and thus raced
> with the cgroup code. Solve this by moving the check under the rq->lock.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> include/linux/cgroup.h | 20 +++++---
> kernel/sched.c | 115 +++++++++++++++++++++++++------------------------
> 2 files changed, 73 insertions(+), 62 deletions(-)
>
> Index: linux-2.6/include/linux/cgroup.h
> ===================================================================
> --- linux-2.6.orig/include/linux/cgroup.h
> +++ linux-2.6/include/linux/cgroup.h
> @@ -525,13 +525,21 @@ static inline struct 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,
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -306,52 +306,6 @@ static int init_task_group_load = INIT_T
> */
> struct task_group init_task_group;
>
> -/* return group to which a task belongs */
> -static inline struct task_group *task_group(struct task_struct *p)
> -{
> - struct task_group *tg;
> -
> -#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;
> -}
> -
> -/* 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];
> -#endif
> -
> -#ifdef CONFIG_RT_GROUP_SCHED
> - p->rt.rt_rq = task_group(p)->rt_rq[cpu];
> - p->rt.parent = task_group(p)->rt_se[cpu];
> -#endif
> - rcu_read_unlock();
> -}
> -
> -#else
> -
> -static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { }
> -static inline struct task_group *task_group(struct task_struct *p)
> -{
> - return NULL;
> -}
> -
> #endif /* CONFIG_CGROUP_SCHED */
>
> /* CFS-related fields in a runqueue */
> @@ -644,6 +598,49 @@ static inline int cpu_of(struct rq *rq)
> #define cpu_curr(cpu) (cpu_rq(cpu)->curr)
> #define raw_rq() (&__raw_get_cpu_var(runqueues))
>
> +#ifdef CONFIG_CGROUP_SCHED
> +
> +/*
> + * 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 cgroup_subsys_state *css;
> +
> + 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)
> +{
> +#ifdef CONFIG_FAIR_GROUP_SCHED
> + p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
> + p->se.parent = task_group(p)->se[cpu];
> +#endif
> +
> +#ifdef CONFIG_RT_GROUP_SCHED
> + p->rt.rt_rq = task_group(p)->rt_rq[cpu];
> + p->rt.parent = task_group(p)->rt_se[cpu];
> +#endif
> +}
> +
> +#else /* CONFIG_CGROUP_SCHED */
> +
> +static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { }
> +static inline struct task_group *task_group(struct task_struct *p)
> +{
> + return NULL;
> +}
> +
> +#endif /* CONFIG_CGROUP_SCHED */
> +
> inline void update_rq_clock(struct rq *rq)
> {
> if (!rq->skip_clock_update)
> @@ -4465,16 +4462,6 @@ 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 +4477,22 @@ recheck:
> * runqueue lock must be held.
> */
> rq = __task_rq_lock(p);
> +
> +#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) {
> + __task_rq_unlock(rq);
> + raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> + return -EPERM;
> + }
> + }
> +#endif
> +
> /* recheck policy now with rq lock held */
> if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
> policy = oldpolicy = -1;
>
>
Sorry. I misunderstood this message when I first read it. I didn't
realize this message include a new version of the patch.
Anyhow, I just tried to apply the patch to 2.6.35-rc2-git3 and got this:
# patch -p1 -l -F 20 --dry-run < ../5.patch
patching file include/linux/cgroup.h
patching file kernel/sched.c
Hunk #1 succeeded at 306 with fuzz 1.
Hunk #3 FAILED at 4462.
Hunk #4 succeeded at 4487 with fuzz 3.
1 out of 4 hunks FAILED -- saving rejects to file kernel/sched.c.rej
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