Commit 710da3c8 authored by Juri Lelli's avatar Juri Lelli Committed by Ingo Molnar
Browse files

sched/core: Prevent race condition between cpuset and __sched_setscheduler() 



No synchronisation mechanism exists between the cpuset subsystem and
calls to function __sched_setscheduler(). As such, it is possible that
new root domains are created on the cpuset side while a deadline
acceptance test is carried out in __sched_setscheduler(), leading to a
potential oversell of CPU bandwidth.

Grab cpuset_rwsem read lock from core scheduler, so to prevent
situations such as the one described above from happening.

The only exception is normalize_rt_tasks() which needs to work under
tasklist_lock and can't therefore grab cpuset_rwsem. We are fine with
this, as this function is only called by sysrq and, if that gets
triggered, DEADLINE guarantees are already gone out of the window
anyway.

Tested-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bristot@redhat.com
Cc: claudio@evidence.eu.com
Cc: lizefan@huawei.com
Cc: longman@redhat.com
Cc: luca.abeni@santannapisa.it
Cc: mathieu.poirier@linaro.org
Cc: rostedt@goodmis.org
Cc: tj@kernel.org
Cc: tommaso.cucinotta@santannapisa.it
Link: https://lkml.kernel.org/r/20190719140000.31694-9-juri.lelli@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1a763fd7

include/linux/cpuset.h

+5 −0
Original line number Original line Diff line number Diff line
@@ -55,6 +55,8 @@ extern void cpuset_init_smp(void); 
extern void cpuset_force_rebuild(void);

extern void cpuset_force_rebuild(void);

extern void cpuset_update_active_cpus(void);

extern void cpuset_update_active_cpus(void);

extern void cpuset_wait_for_hotplug(void);

extern void cpuset_wait_for_hotplug(void);

extern void cpuset_read_lock(void);

extern void cpuset_read_unlock(void);

extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);

extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);

extern void cpuset_cpus_allowed_fallback(struct task_struct *p);

extern void cpuset_cpus_allowed_fallback(struct task_struct *p);

extern nodemask_t cpuset_mems_allowed(struct task_struct *p);

extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
@@ -176,6 +178,9 @@ static inline void cpuset_update_active_cpus(void) 




static inline void cpuset_wait_for_hotplug(void) { }

static inline void cpuset_wait_for_hotplug(void) { }





static inline void cpuset_read_lock(void) { }

static inline void cpuset_read_unlock(void) { }



static inline void cpuset_cpus_allowed(struct task_struct *p,

static inline void cpuset_cpus_allowed(struct task_struct *p,

				       struct cpumask *mask)

				       struct cpumask *mask)

{

{

kernel/cgroup/cpuset.c

+11 −0
Original line number Original line Diff line number Diff line
@@ -334,6 +334,17 @@ static struct cpuset top_cpuset = { 
 */

 */





DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);

DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);



void cpuset_read_lock(void)

{

	percpu_down_read(&cpuset_rwsem);

}



void cpuset_read_unlock(void)

{

	percpu_up_read(&cpuset_rwsem);

}



static DEFINE_SPINLOCK(callback_lock);

static DEFINE_SPINLOCK(callback_lock);





static struct workqueue_struct *cpuset_migrate_mm_wq;

static struct workqueue_struct *cpuset_migrate_mm_wq;

kernel/sched/core.c

+17 −3
Original line number Original line Diff line number Diff line
@@ -4698,6 +4698,9 @@ recheck: 
			return retval;

			return retval;

	}

	}





	if (pi)

		cpuset_read_lock();



	/*

	/*

	 * Make sure no PI-waiters arrive (or leave) while we are

	 * Make sure no PI-waiters arrive (or leave) while we are

	 * changing the priority of the task:

	 * changing the priority of the task:
@@ -4772,6 +4775,8 @@ change: 
	if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {

	if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {

		policy = oldpolicy = -1;

		policy = oldpolicy = -1;

		task_rq_unlock(rq, p, &rf);

		task_rq_unlock(rq, p, &rf);

		if (pi)

			cpuset_read_unlock();

		goto recheck;

		goto recheck;

	}

	}
@@ -4832,8 +4837,10 @@ change: 
	preempt_disable();

	preempt_disable();

	task_rq_unlock(rq, p, &rf);

	task_rq_unlock(rq, p, &rf);





	if (pi)

	if (pi) {

		cpuset_read_unlock();

		rt_mutex_adjust_pi(p);

		rt_mutex_adjust_pi(p);

	}





	/* Run balance callbacks after we've adjusted the PI chain: */

	/* Run balance callbacks after we've adjusted the PI chain: */

	balance_callback(rq);

	balance_callback(rq);
@@ -4843,6 +4850,8 @@ change: 




unlock:

unlock:

	task_rq_unlock(rq, p, &rf);

	task_rq_unlock(rq, p, &rf);

	if (pi)

		cpuset_read_unlock();

	return retval;

	return retval;

}

}
@@ -4927,10 +4936,15 @@ do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param) 
	rcu_read_lock();

	rcu_read_lock();

	retval = -ESRCH;

	retval = -ESRCH;

	p = find_process_by_pid(pid);

	p = find_process_by_pid(pid);

	if (p != NULL)

	if (likely(p))

		retval = sched_setscheduler(p, policy, &lparam);

		get_task_struct(p);

	rcu_read_unlock();

	rcu_read_unlock();





	if (likely(p)) {

		retval = sched_setscheduler(p, policy, &lparam);

		put_task_struct(p);

	}



	return retval;

	return retval;

}

}

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