Commit a5bd6ba3 authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Use cgroup_lock/unlock() to synchronize against cgroup operations 



SCX hooks into CPU cgroup controller operations and read-locks
scx_cgroup_rwsem to exclude them while enabling and disable schedulers.
While this works, it's unnecessarily complicated given that
cgroup_[un]lock() are available and thus the cgroup operations can be locked
out that way.

Drop scx_cgroup_rwsem locking from the tg on/offline and cgroup [can_]attach
operations. Instead, grab cgroup_lock() from scx_cgroup_lock(). Drop
scx_cgroup_finish_attach() which is no longer necessary. Drop the now
unnecessary rcu locking and css ref bumping in scx_cgroup_init() and
scx_cgroup_exit().

As scx_cgroup_set_weight/bandwidth() paths aren't protected by
cgroup_lock(), rename scx_cgroup_rwsem to scx_cgroup_ops_rwsem and retain
the locking there.

This is overall simpler and will also allow enable/disable paths to
synchronize against cgroup changes independent of the CPU controller.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: default avatarAndrea Righi <arighi@nvidia.com>
parent bcb7c230

kernel/sched/core.c

+0 −2
Original line number Diff line number Diff line
@@ -9362,8 +9362,6 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset) 


	cgroup_taskset_for_each(task, css, tset)

		sched_move_task(task, false);



	scx_cgroup_finish_attach();

}



static void cpu_cgroup_cancel_attach(struct cgroup_taskset *tset)

kernel/sched/ext.c

+14 −52
Original line number Diff line number Diff line
@@ -3055,7 +3055,7 @@ bool scx_can_stop_tick(struct rq *rq) 


#ifdef CONFIG_EXT_GROUP_SCHED



DEFINE_STATIC_PERCPU_RWSEM(scx_cgroup_rwsem);

DEFINE_STATIC_PERCPU_RWSEM(scx_cgroup_ops_rwsem);

static bool scx_cgroup_enabled;



void scx_tg_init(struct task_group *tg)
@@ -3072,8 +3072,6 @@ int scx_tg_online(struct task_group *tg) 


	WARN_ON_ONCE(tg->scx.flags & (SCX_TG_ONLINE | SCX_TG_INITED));



	percpu_down_read(&scx_cgroup_rwsem);



	if (scx_cgroup_enabled) {

		if (SCX_HAS_OP(sch, cgroup_init)) {

			struct scx_cgroup_init_args args =
@@ -3093,7 +3091,6 @@ int scx_tg_online(struct task_group *tg) 
		tg->scx.flags |= SCX_TG_ONLINE;

	}



	percpu_up_read(&scx_cgroup_rwsem);

	return ret;

}
@@ -3103,15 +3100,11 @@ void scx_tg_offline(struct task_group *tg) 


	WARN_ON_ONCE(!(tg->scx.flags & SCX_TG_ONLINE));



	percpu_down_read(&scx_cgroup_rwsem);



	if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_exit) &&

	    (tg->scx.flags & SCX_TG_INITED))

		SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_exit, NULL,

			    tg->css.cgroup);

	tg->scx.flags &= ~(SCX_TG_ONLINE | SCX_TG_INITED);



	percpu_up_read(&scx_cgroup_rwsem);

}



int scx_cgroup_can_attach(struct cgroup_taskset *tset)
@@ -3121,9 +3114,6 @@ int scx_cgroup_can_attach(struct cgroup_taskset *tset) 
	struct task_struct *p;

	int ret;



	/* released in scx_finish/cancel_attach() */

	percpu_down_read(&scx_cgroup_rwsem);



	if (!scx_cgroup_enabled)

		return 0;
@@ -3163,7 +3153,6 @@ int scx_cgroup_can_attach(struct cgroup_taskset *tset) 
		p->scx.cgrp_moving_from = NULL;

	}



	percpu_up_read(&scx_cgroup_rwsem);

	return ops_sanitize_err(sch, "cgroup_prep_move", ret);

}
@@ -3186,11 +3175,6 @@ void scx_cgroup_move_task(struct task_struct *p) 
	p->scx.cgrp_moving_from = NULL;

}



void scx_cgroup_finish_attach(void)

{

	percpu_up_read(&scx_cgroup_rwsem);

}



void scx_cgroup_cancel_attach(struct cgroup_taskset *tset)

{

	struct scx_sched *sch = scx_root;
@@ -3198,7 +3182,7 @@ void scx_cgroup_cancel_attach(struct cgroup_taskset *tset) 
	struct task_struct *p;



	if (!scx_cgroup_enabled)

		goto out_unlock;

		return;



	cgroup_taskset_for_each(p, css, tset) {

		if (SCX_HAS_OP(sch, cgroup_cancel_move) &&
@@ -3207,15 +3191,13 @@ void scx_cgroup_cancel_attach(struct cgroup_taskset *tset) 
				    p, p->scx.cgrp_moving_from, css->cgroup);

		p->scx.cgrp_moving_from = NULL;

	}

out_unlock:

	percpu_up_read(&scx_cgroup_rwsem);

}



void scx_group_set_weight(struct task_group *tg, unsigned long weight)

{

	struct scx_sched *sch = scx_root;



	percpu_down_read(&scx_cgroup_rwsem);

	percpu_down_read(&scx_cgroup_ops_rwsem);



	if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_weight) &&

	    tg->scx.weight != weight)
@@ -3224,7 +3206,7 @@ void scx_group_set_weight(struct task_group *tg, unsigned long weight) 


	tg->scx.weight = weight;



	percpu_up_read(&scx_cgroup_rwsem);

	percpu_up_read(&scx_cgroup_ops_rwsem);

}



void scx_group_set_idle(struct task_group *tg, bool idle)
@@ -3237,7 +3219,7 @@ void scx_group_set_bandwidth(struct task_group *tg, 
{

	struct scx_sched *sch = scx_root;



	percpu_down_read(&scx_cgroup_rwsem);

	percpu_down_read(&scx_cgroup_ops_rwsem);



	if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_bandwidth) &&

	    (tg->scx.bw_period_us != period_us ||
@@ -3250,23 +3232,25 @@ void scx_group_set_bandwidth(struct task_group *tg, 
	tg->scx.bw_quota_us = quota_us;

	tg->scx.bw_burst_us = burst_us;



	percpu_up_read(&scx_cgroup_rwsem);

	percpu_up_read(&scx_cgroup_ops_rwsem);

}



static void scx_cgroup_lock(void)

{

	percpu_down_write(&scx_cgroup_rwsem);

	percpu_down_write(&scx_cgroup_ops_rwsem);

	cgroup_lock();

}



static void scx_cgroup_unlock(void)

{

	percpu_up_write(&scx_cgroup_rwsem);

	cgroup_unlock();

	percpu_up_write(&scx_cgroup_ops_rwsem);

}



#else	/* CONFIG_EXT_GROUP_SCHED */



static inline void scx_cgroup_lock(void) {}

static inline void scx_cgroup_unlock(void) {}

static void scx_cgroup_lock(void) {}

static void scx_cgroup_unlock(void) {}



#endif	/* CONFIG_EXT_GROUP_SCHED */
@@ -3382,15 +3366,12 @@ static void scx_cgroup_exit(struct scx_sched *sch) 
{

	struct cgroup_subsys_state *css;



	percpu_rwsem_assert_held(&scx_cgroup_rwsem);



	scx_cgroup_enabled = false;



	/*

	 * scx_tg_on/offline() are excluded through scx_cgroup_rwsem. If we walk

	 * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk

	 * cgroups and exit all the inited ones, all online cgroups are exited.

	 */

	rcu_read_lock();

	css_for_each_descendant_post(css, &root_task_group.css) {

		struct task_group *tg = css_tg(css);
@@ -3401,17 +3382,9 @@ static void scx_cgroup_exit(struct scx_sched *sch) 
		if (!sch->ops.cgroup_exit)

			continue;



		if (WARN_ON_ONCE(!css_tryget(css)))

			continue;

		rcu_read_unlock();



		SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_exit, NULL,

			    css->cgroup);



		rcu_read_lock();

		css_put(css);

	}

	rcu_read_unlock();

}



static int scx_cgroup_init(struct scx_sched *sch)
@@ -3419,13 +3392,10 @@ static int scx_cgroup_init(struct scx_sched *sch) 
	struct cgroup_subsys_state *css;

	int ret;



	percpu_rwsem_assert_held(&scx_cgroup_rwsem);



	/*

	 * scx_tg_on/offline() are excluded through scx_cgroup_rwsem. If we walk

	 * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk

	 * cgroups and init, all online cgroups are initialized.

	 */

	rcu_read_lock();

	css_for_each_descendant_pre(css, &root_task_group.css) {

		struct task_group *tg = css_tg(css);

		struct scx_cgroup_init_args args = {
@@ -3444,10 +3414,6 @@ static int scx_cgroup_init(struct scx_sched *sch) 
			continue;

		}



		if (WARN_ON_ONCE(!css_tryget(css)))

			continue;

		rcu_read_unlock();



		ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, cgroup_init, NULL,

				      css->cgroup, &args);

		if (ret) {
@@ -3456,11 +3422,7 @@ static int scx_cgroup_init(struct scx_sched *sch) 
			return ret;

		}

		tg->scx.flags |= SCX_TG_INITED;



		rcu_read_lock();

		css_put(css);

	}

	rcu_read_unlock();



	WARN_ON_ONCE(scx_cgroup_enabled);

	scx_cgroup_enabled = true;

kernel/sched/ext.h

+0 −2
Original line number Diff line number Diff line
@@ -77,7 +77,6 @@ int scx_tg_online(struct task_group *tg); 
void scx_tg_offline(struct task_group *tg);

int scx_cgroup_can_attach(struct cgroup_taskset *tset);

void scx_cgroup_move_task(struct task_struct *p);

void scx_cgroup_finish_attach(void);

void scx_cgroup_cancel_attach(struct cgroup_taskset *tset);

void scx_group_set_weight(struct task_group *tg, unsigned long cgrp_weight);

void scx_group_set_idle(struct task_group *tg, bool idle);
@@ -88,7 +87,6 @@ static inline int scx_tg_online(struct task_group *tg) { return 0; } 
static inline void scx_tg_offline(struct task_group *tg) {}

static inline int scx_cgroup_can_attach(struct cgroup_taskset *tset) { return 0; }

static inline void scx_cgroup_move_task(struct task_struct *p) {}

static inline void scx_cgroup_finish_attach(void) {}

static inline void scx_cgroup_cancel_attach(struct cgroup_taskset *tset) {}

static inline void scx_group_set_weight(struct task_group *tg, unsigned long cgrp_weight) {}

static inline void scx_group_set_idle(struct task_group *tg, bool idle) {}