From f82f80426f7afcf55953924e71555984a4bd6ce6 Mon Sep 17 00:00:00 2001 From: Juri Lelli Date: Tue, 7 Oct 2014 09:52:11 +0100 Subject: [PATCH] sched/deadline: Ensure that updates to exclusive cpusets don't break AC How we deal with updates to exclusive cpusets is currently broken. As an example, suppose we have an exclusive cpuset composed of two cpus: A[cpu0,cpu1]. We can assign SCHED_DEADLINE task to it up to the allowed bandwidth. If we want now to modify cpusetA's cpumask, we have to check that removing a cpu's amount of bandwidth doesn't break AC guarantees. This thing isn't checked in the current code. This patch fixes the problem above, denying an update if the new cpumask won't have enough bandwidth for SCHED_DEADLINE tasks that are currently active. Signed-off-by: Juri Lelli Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Li Zefan Cc: cgroups@vger.kernel.org Link: http://lkml.kernel.org/r/5433E6AF.5080105@arm.com Signed-off-by: Ingo Molnar --- include/linux/sched.h | 2 ++ kernel/cpuset.c | 10 ++++++++++ kernel/sched/core.c | 19 +++++++++++++++++++ 3 files changed, 31 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index 1d1fa081d44f..320a9779f1b4 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2052,6 +2052,8 @@ static inline void tsk_restore_flags(struct task_struct *task, task->flags |= orig_flags & flags; } +extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, + const struct cpumask *trial); extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed); #ifdef CONFIG_SMP diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 7af8577fc8f8..723cfc9d0ad7 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -506,6 +506,16 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial) goto out; } + /* + * We can't shrink if we won't have enough room for SCHED_DEADLINE + * tasks. + */ + ret = -EBUSY; + if (is_cpu_exclusive(cur) && + !cpuset_cpumask_can_shrink(cur->cpus_allowed, + trial->cpus_allowed)) + goto out; + ret = 0; out: rcu_read_unlock(); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 9993feeb8b10..0456a55fc27f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4650,6 +4650,25 @@ void init_idle(struct task_struct *idle, int cpu) #endif } +int cpuset_cpumask_can_shrink(const struct cpumask *cur, + const struct cpumask *trial) +{ + int ret = 1, trial_cpus; + struct dl_bw *cur_dl_b; + unsigned long flags; + + cur_dl_b = dl_bw_of(cpumask_any(cur)); + trial_cpus = cpumask_weight(trial); + + raw_spin_lock_irqsave(&cur_dl_b->lock, flags); + if (cur_dl_b->bw != -1 && + cur_dl_b->bw * trial_cpus < cur_dl_b->total_bw) + ret = 0; + raw_spin_unlock_irqrestore(&cur_dl_b->lock, flags); + + return ret; +} + int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed) {