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Commit 14a40ffc authored by Tejun Heo's avatar Tejun Heo
Browse files

sched: replace PF_THREAD_BOUND with PF_NO_SETAFFINITY 



PF_THREAD_BOUND was originally used to mark kernel threads which were
bound to a specific CPU using kthread_bind() and a task with the flag
set allows cpus_allowed modifications only to itself.  Workqueue is
currently abusing it to prevent userland from meddling with
cpus_allowed of workqueue workers.

What we need is a flag to prevent userland from messing with
cpus_allowed of certain kernel tasks.  In kernel, anyone can
(incorrectly) squash the flag, and, for worker-type usages,
restricting cpus_allowed modification to the task itself doesn't
provide meaningful extra proection as other tasks can inject work
items to the task anyway.

This patch replaces PF_THREAD_BOUND with PF_NO_SETAFFINITY.
sched_setaffinity() checks the flag and return -EINVAL if set.
set_cpus_allowed_ptr() is no longer affected by the flag.

This will allow simplifying workqueue worker CPU affinity management.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
parent 2e109a28

include/linux/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -1793,7 +1793,7 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, 
#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_NO_SETAFFINITY 0x04000000	/* Userland is not allowed to meddle with cpus_allowed */

#define PF_MCE_EARLY    0x08000000      /* Early kill for mce process policy */

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

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

kernel/cgroup.c

+2 −2
Original line number Diff line number Diff line
@@ -2224,11 +2224,11 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup) 
		tsk = tsk->group_leader;



	/*

	 * Workqueue threads may acquire PF_THREAD_BOUND and become

	 * Workqueue threads may acquire PF_NO_SETAFFINITY and become

	 * trapped in a cpuset, or RT worker may be born in a cgroup

	 * with no rt_runtime allocated.  Just say no.

	 */

	if (tsk == kthreadd_task || (tsk->flags & PF_THREAD_BOUND)) {

	if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {

		ret = -EINVAL;

		rcu_read_unlock();

		goto out_unlock_cgroup;

kernel/cpuset.c

+8 −8
Original line number Diff line number Diff line
@@ -1388,16 +1388,16 @@ static int cpuset_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset) 


	cgroup_taskset_for_each(task, cgrp, tset) {

		/*

		 * Kthreads bound to specific cpus cannot be moved to a new

		 * cpuset; we cannot change their cpu affinity and

		 * isolating such threads by their set of allowed nodes is

		 * unnecessary.  Thus, cpusets are not applicable for such

		 * threads.  This prevents checking for success of

		 * set_cpus_allowed_ptr() on all attached tasks before

		 * cpus_allowed may be changed.

		 * Kthreads which disallow setaffinity shouldn't be moved

		 * to a new cpuset; we don't want to change their cpu

		 * affinity and isolating such threads by their set of

		 * allowed nodes is unnecessary.  Thus, cpusets are not

		 * applicable for such threads.  This prevents checking for

		 * success of set_cpus_allowed_ptr() on all attached tasks

		 * before cpus_allowed may be changed.

		 */

		ret = -EINVAL;

		if (task->flags & PF_THREAD_BOUND)

		if (task->flags & PF_NO_SETAFFINITY)

			goto out_unlock;

		ret = security_task_setscheduler(task);

		if (ret)

kernel/kthread.c

+1 −1
Original line number Diff line number Diff line
@@ -260,7 +260,7 @@ static void __kthread_bind(struct task_struct *p, unsigned int cpu) 
{

	/* It's safe because the task is inactive. */

	do_set_cpus_allowed(p, cpumask_of(cpu));

	p->flags |= PF_THREAD_BOUND;

	p->flags |= PF_NO_SETAFFINITY;

}



/**

kernel/sched/core.c

+4 −5
Original line number Diff line number Diff line
@@ -4126,6 +4126,10 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask) 
	get_task_struct(p);

	rcu_read_unlock();



	if (p->flags & PF_NO_SETAFFINITY) {

		retval = -EINVAL;

		goto out_put_task;

	}

	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {

		retval = -ENOMEM;

		goto out_put_task;
@@ -4773,11 +4777,6 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask) 
		goto out;

	}



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

		ret = -EINVAL;

		goto out;

	}



	do_set_cpus_allowed(p, new_mask);



	/* Can the task run on the task's current CPU? If so, we're done */