Commit 71d7847c authored by Andrea Righi's avatar Andrea Righi Committed by Tejun Heo
Browse files

sched_ext: Fix scx_bpf_dsq_peek() with FIFO DSQs 



When removing a task from a FIFO DSQ, we must delete it from the list
before updating dsq->first_task, otherwise the following lookup will
just re-read the same task, leaving first_task pointing to removed
entry.

This issue only affects DSQs operating in FIFO mode, as priority DSQs
correctly update the rbtree before re-evaluating the new first task.

Remove the item from the list before refreshing the first task to
guarantee the correct behavior in FIFO DSQs.

Fixes: 44f5c8ec ("sched_ext: Add lockless peek operation for DSQs")
Signed-off-by: default avatarAndrea Righi <arighi@nvidia.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent e6770882

kernel/sched/ext.c

+3 −3
Original line number Diff line number Diff line
@@ -1044,15 +1044,15 @@ static void task_unlink_from_dsq(struct task_struct *p, 
		p->scx.dsq_flags &= ~SCX_TASK_DSQ_ON_PRIQ;

	}



	list_del_init(&p->scx.dsq_list.node);

	dsq_mod_nr(dsq, -1);



	if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN) && dsq->first_task == p) {

		struct task_struct *first_task;



		first_task = nldsq_next_task(dsq, NULL, false);

		rcu_assign_pointer(dsq->first_task, first_task);

	}



	list_del_init(&p->scx.dsq_list.node);

	dsq_mod_nr(dsq, -1);

}



static void dispatch_dequeue(struct rq *rq, struct task_struct *p)