From dc61b1d65e353d638b2445f71fb8e5b5630f2415 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 8 Jun 2010 11:40:42 +0200 Subject: sched: Fix PROVE_RCU vs cpu_cgroup 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 derefence 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 appropriate lock. Signed-off-by: Peter Zijlstra Cc: "Paul E. McKenney" LKML-Reference: Signed-off-by: Ingo Molnar --- kernel/sched.c | 115 +++++++++++++++++++++++++++++---------------------------- 1 file changed, 59 insertions(+), 56 deletions(-) (limited to 'kernel') diff --git a/kernel/sched.c b/kernel/sched.c index f8b8996228dd..2aaceebd484c 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -306,52 +306,6 @@ static int init_task_group_load = INIT_TASK_GROUP_LOAD; */ 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; -- cgit v1.2.3 From 3c93717cfa51316e4dbb471e7c0f9d243359d5f8 Mon Sep 17 00:00:00 2001 From: Alex,Shi Date: Thu, 17 Jun 2010 14:08:13 +0800 Subject: sched: Fix over-scheduling bug Commit e70971591 ("sched: Optimize unused cgroup configuration") introduced an imbalanced scheduling bug. If we do not use CGROUP, function update_h_load won't update h_load. When the system has a large number of tasks far more than logical CPU number, the incorrect cfs_rq[cpu]->h_load value will cause load_balance() to pull too many tasks to the local CPU from the busiest CPU. So the busiest CPU keeps going in a round robin. That will hurt performance. The issue was found originally by a scientific calculation workload that developed by Yanmin. With that commit, the workload performance drops about 40%. CPU before after 00 : 2 : 7 01 : 1 : 7 02 : 11 : 6 03 : 12 : 7 04 : 6 : 6 05 : 11 : 7 06 : 10 : 6 07 : 12 : 7 08 : 11 : 6 09 : 12 : 6 10 : 1 : 6 11 : 1 : 6 12 : 6 : 6 13 : 2 : 6 14 : 2 : 6 15 : 1 : 6 Reviewed-by: Yanmin zhang Signed-off-by: Alex Shi Signed-off-by: Peter Zijlstra LKML-Reference: <1276754893.9452.5442.camel@debian> Signed-off-by: Ingo Molnar --- kernel/sched.c | 3 --- 1 file changed, 3 deletions(-) (limited to 'kernel') diff --git a/kernel/sched.c b/kernel/sched.c index 2aaceebd484c..6c9e7c8735bf 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1657,9 +1657,6 @@ static void update_shares(struct sched_domain *sd) static void update_h_load(long cpu) { - if (root_task_group_empty()) - return; - walk_tg_tree(tg_load_down, tg_nop, (void *)cpu); } -- cgit v1.2.3 From 0d98bb2656e9bd2dfda2d089db1fe1dbdab41504 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Mon, 24 May 2010 12:11:43 -0700 Subject: sched: Prevent compiler from optimising the sched_avg_update() loop GCC 4.4.1 on ARM has been observed to replace the while loop in sched_avg_update with a call to uldivmod, resulting in the following build failure at link-time: kernel/built-in.o: In function `sched_avg_update': kernel/sched.c:1261: undefined reference to `__aeabi_uldivmod' kernel/sched.c:1261: undefined reference to `__aeabi_uldivmod' make: *** [.tmp_vmlinux1] Error 1 This patch introduces a fake data hazard to the loop body to prevent the compiler optimising the loop away. Signed-off-by: Will Deacon Signed-off-by: Andrew Morton Acked-by: Peter Zijlstra Cc: Catalin Marinas Cc: Russell King Cc: Linus Torvalds Cc: Signed-off-by: Ingo Molnar --- kernel/sched.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'kernel') diff --git a/kernel/sched.c b/kernel/sched.c index 6c9e7c8735bf..a24d6d5d83f6 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1254,6 +1254,12 @@ static void sched_avg_update(struct rq *rq) s64 period = sched_avg_period(); while ((s64)(rq->clock - rq->age_stamp) > period) { + /* + * Inline assembly required to prevent the compiler + * optimising this loop into a divmod call. + * See __iter_div_u64_rem() for another example of this. + */ + asm("" : "+rm" (rq->age_stamp)); rq->age_stamp += period; rq->rt_avg /= 2; } -- cgit v1.2.3