Commit e99129e5 authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Allow p->scx.disallow only while loading 



From 1232da7eced620537a78f19c8cf3d4a3508e2419 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Wed, 31 Jul 2024 09:14:52 -1000

p->scx.disallow provides a way for the BPF scheduler to reject certain tasks
from attaching. It's currently allowed for both the load and fork paths;
however, the latter doesn't actually work as p->sched_class is already set
by the time scx_ops_init_task() is called during fork.

This is a convenience feature which is mostly useful from the load path
anyway. Allow it only from the load path.

v2: Trigger scx_ops_error() iff @p->policy == SCHED_EXT to make it a bit
    easier for the BPF scheduler (David).

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-by: default avatar"Zhangqiao (2012 lab)" <zhangqiao22@huawei.com>
Link: http://lkml.kernel.org/r/20240711110720.1285-1-zhangqiao22@huawei.com


Fixes: 7bb6f081 ("sched_ext: Allow BPF schedulers to disallow specific tasks from joining SCHED_EXT")
Acked-by: default avatarDavid Vernet <void@manifault.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent a2f4b16e

include/linux/sched/ext.h

+6 −5
Original line number Diff line number Diff line
@@ -179,11 +179,12 @@ struct sched_ext_entity { 
	 * If set, reject future sched_setscheduler(2) calls updating the policy

	 * to %SCHED_EXT with -%EACCES.

	 *

	 * If set from ops.init_task() and the task's policy is already

	 * %SCHED_EXT, which can happen while the BPF scheduler is being loaded

	 * or by inhering the parent's policy during fork, the task's policy is

	 * rejected and forcefully reverted to %SCHED_NORMAL. The number of

	 * such events are reported through /sys/kernel/debug/sched_ext::nr_rejected.

	 * Can be set from ops.init_task() while the BPF scheduler is being

	 * loaded (!scx_init_task_args->fork). If set and the task's policy is

	 * already %SCHED_EXT, the task's policy is rejected and forcefully

	 * reverted to %SCHED_NORMAL. The number of such events are reported

	 * through /sys/kernel/debug/sched_ext::nr_rejected. Setting this flag

	 * during fork is not allowed.

	 */

	bool			disallow;	/* reject switching into SCX */

kernel/sched/ext.c

+20 −15
Original line number Diff line number Diff line
@@ -3396,17 +3396,18 @@ static int scx_ops_init_task(struct task_struct *p, struct task_group *tg, bool 
	scx_set_task_state(p, SCX_TASK_INIT);



	if (p->scx.disallow) {

		if (!fork) {

			struct rq *rq;

			struct rq_flags rf;



			rq = task_rq_lock(p, &rf);



			/*

		 * We're either in fork or load path and @p->policy will be

		 * applied right after. Reverting @p->policy here and rejecting

			 * We're in the load path and @p->policy will be applied

			 * right after. Reverting @p->policy here and rejecting

			 * %SCHED_EXT transitions from scx_check_setscheduler()

		 * guarantees that if ops.init_task() sets @p->disallow, @p can

		 * never be in SCX.

			 * guarantees that if ops.init_task() sets @p->disallow,

			 * @p can never be in SCX.

			 */

			if (p->policy == SCHED_EXT) {

				p->policy = SCHED_NORMAL;
@@ -3414,6 +3415,10 @@ static int scx_ops_init_task(struct task_struct *p, struct task_group *tg, bool 
			}



			task_rq_unlock(rq, p, &rf);

		} else if (p->policy == SCHED_EXT) {

			scx_ops_error("ops.init_task() set task->scx.disallow for %s[%d] during fork",

				      p->comm, p->pid);

		}

	}



	p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT;