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Commit f82f8042 authored by Juri Lelli's avatar Juri Lelli Committed by Ingo Molnar
Browse files

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: default avatarJuri Lelli <juri.lelli@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: cgroups@vger.kernel.org
Link: http://lkml.kernel.org/r/5433E6AF.5080105@arm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 7f51412a

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -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

kernel/cpuset.c

+10 −0
Original line number Diff line number Diff line
@@ -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();

kernel/sched/core.c

+19 −0
Original line number Diff line number Diff line
@@ -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)

{