Commit f4a6c506 authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Always bounce scx_disable() through irq_work 



scx_disable() directly called kthread_queue_work() which can acquire
worker->lock, pi_lock and rq->__lock. This made scx_disable() unsafe to
call while holding locks that conflict with this chain - in particular,
scx_claim_exit() calls scx_disable() for each descendant while holding
scx_sched_lock, which nests inside rq->__lock in scx_bypass().

The error path (scx_vexit()) was already bouncing through irq_work to
avoid this issue. Generalize the pattern to all scx_disable() calls by
always going through irq_work. irq_work_queue() is lockless and safe to
call from any context, and the actual kthread_queue_work() call happens
in the irq_work handler outside any locks.

Rename error_irq_work to disable_irq_work to reflect the broader usage.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarAndrea Righi <arighi@nvidia.com>
parent b5bc0435

kernel/sched/ext.c

+6 −6
Original line number Diff line number Diff line
@@ -4498,7 +4498,7 @@ static void scx_sched_free_rcu_work(struct work_struct *work) 
	struct scx_dispatch_q *dsq;

	int cpu, node;



	irq_work_sync(&sch->error_irq_work);

	irq_work_sync(&sch->disable_irq_work);

	kthread_destroy_worker(sch->helper);

	timer_shutdown_sync(&sch->bypass_lb_timer);
@@ -5679,7 +5679,7 @@ static void scx_disable(struct scx_sched *sch, enum scx_exit_kind kind) 
{

	guard(preempt)();

	if (scx_claim_exit(sch, kind))

		kthread_queue_work(sch->helper, &sch->disable_work);

		irq_work_queue(&sch->disable_irq_work);

}



static void dump_newline(struct seq_buf *s)
@@ -6012,9 +6012,9 @@ static void scx_dump_state(struct scx_sched *sch, struct scx_exit_info *ei, 
		       trunc_marker, sizeof(trunc_marker));

}



static void scx_error_irq_workfn(struct irq_work *irq_work)

static void scx_disable_irq_workfn(struct irq_work *irq_work)

{

	struct scx_sched *sch = container_of(irq_work, struct scx_sched, error_irq_work);

	struct scx_sched *sch = container_of(irq_work, struct scx_sched, disable_irq_work);

	struct scx_exit_info *ei = sch->exit_info;



	if (ei->kind >= SCX_EXIT_ERROR)
@@ -6048,7 +6048,7 @@ static bool scx_vexit(struct scx_sched *sch, 
	ei->kind = kind;

	ei->reason = scx_exit_reason(ei->kind);



	irq_work_queue(&sch->error_irq_work);

	irq_work_queue(&sch->disable_irq_work);

	return true;

}
@@ -6184,7 +6184,7 @@ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops, 


	sch->slice_dfl = SCX_SLICE_DFL;

	atomic_set(&sch->exit_kind, SCX_EXIT_NONE);

	init_irq_work(&sch->error_irq_work, scx_error_irq_workfn);

	init_irq_work(&sch->disable_irq_work, scx_disable_irq_workfn);

	kthread_init_work(&sch->disable_work, scx_disable_workfn);

	timer_setup(&sch->bypass_lb_timer, scx_bypass_lb_timerfn, 0);

	sch->ops = *ops;

kernel/sched/ext_internal.h

+1 −1
Original line number Diff line number Diff line
@@ -1042,7 +1042,7 @@ struct scx_sched { 
	struct kobject		kobj;



	struct kthread_worker	*helper;

	struct irq_work		error_irq_work;

	struct irq_work		disable_irq_work;

	struct kthread_work	disable_work;

	struct timer_list	bypass_lb_timer;

	struct rcu_work		rcu_work;