Commit 9985b0ba authored by David Rientjes's avatar David Rientjes Committed by Ingo Molnar
Browse files

sched: prevent bound kthreads from changing cpus_allowed 



Kthreads that have called kthread_bind() are bound to specific cpus, so
other tasks should not be able to change their cpus_allowed from under
them.  Otherwise, it is possible to move kthreads, such as the migration
or software watchdog threads, so they are not allowed access to the cpu
they work on.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 7def2be1

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1486,6 +1486,7 @@ static inline void put_task_struct(struct task_struct *t) 
#define PF_SWAPWRITE	0x00800000	/* Allowed to write to swap */

#define PF_SPREAD_PAGE	0x01000000	/* Spread page cache over cpuset */

#define PF_SPREAD_SLAB	0x02000000	/* Spread some slab caches over cpuset */

#define PF_THREAD_BOUND	0x04000000	/* Thread bound to specific cpu */

#define PF_MEMPOLICY	0x10000000	/* Non-default NUMA mempolicy */

#define PF_MUTEX_TESTER	0x20000000	/* Thread belongs to the rt mutex tester */

#define PF_FREEZER_SKIP	0x40000000	/* Freezer should not count it as freezeable */

kernel/cpuset.c

+13 −1
Original line number Diff line number Diff line
@@ -1190,6 +1190,15 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, 


	if (cpus_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))

		return -ENOSPC;

	if (tsk->flags & PF_THREAD_BOUND) {

		cpumask_t mask;



		mutex_lock(&callback_mutex);

		mask = cs->cpus_allowed;

		mutex_unlock(&callback_mutex);

		if (!cpus_equal(tsk->cpus_allowed, mask))

			return -EINVAL;

	}



	return security_task_setscheduler(tsk, 0, NULL);

}
@@ -1203,11 +1212,14 @@ static void cpuset_attach(struct cgroup_subsys *ss, 
	struct mm_struct *mm;

	struct cpuset *cs = cgroup_cs(cont);

	struct cpuset *oldcs = cgroup_cs(oldcont);

	int err;



	mutex_lock(&callback_mutex);

	guarantee_online_cpus(cs, &cpus);

	set_cpus_allowed_ptr(tsk, &cpus);

	err = set_cpus_allowed_ptr(tsk, &cpus);

	mutex_unlock(&callback_mutex);

	if (err)

		return;



	from = oldcs->mems_allowed;

	to = cs->mems_allowed;

kernel/kthread.c

+1 −0
Original line number Diff line number Diff line
@@ -180,6 +180,7 @@ void kthread_bind(struct task_struct *k, unsigned int cpu) 
	set_task_cpu(k, cpu);

	k->cpus_allowed = cpumask_of_cpu(cpu);

	k->rt.nr_cpus_allowed = 1;

	k->flags |= PF_THREAD_BOUND;

}

EXPORT_SYMBOL(kthread_bind);

kernel/sched.c

+6 −0
Original line number Diff line number Diff line
@@ -5563,6 +5563,12 @@ int set_cpus_allowed_ptr(struct task_struct *p, const cpumask_t *new_mask) 
		goto out;

	}



	if (unlikely((p->flags & PF_THREAD_BOUND) && p != current &&

		     !cpus_equal(p->cpus_allowed, *new_mask))) {

		ret = -EINVAL;

		goto out;

	}



	if (p->sched_class->set_cpus_allowed)

		p->sched_class->set_cpus_allowed(p, new_mask);

	else {

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