sched_ext: Use rcu_access_pointer() for the first_task comparison

dsq->first_task is __rcu for the lockless scx_bpf_dsq_peek(). The task removal path compares it against the departing task with a plain load, which sparse flags. The comparison runs under the dsq lock and only tests identity, so rcu_access_pointer() is the fit.

Tejun Heo committed 3 months ago

Commit 6ee471b1 parent ce228341 file · +1 −1Browse files

Showing the changes to kernel (1 of 1 file). Show all

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kernel/sched/ext/ext.c+1−1

@@ -1654,7 +1654,7 @@ static void task_unlink_from_dsq(struct task_struct *p, · 1653 unmodified lines
1654	list_del_init(&p->scx.dsq_list.node);	1654	list_del_init(&p->scx.dsq_list.node);
1655	dsq_dec_nr(dsq, p);	1655	dsq_dec_nr(dsq, p);
1656		1656
1657	if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN) && dsq->first_task == p) {	1657	if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN) && rcu_access_pointer(dsq->first_task) == p) {
1658	struct task_struct *first_task;	1658	struct task_struct *first_task;
1659		1659
1660	first_task = nldsq_next_task(dsq, NULL, false);	1660	first_task = nldsq_next_task(dsq, NULL, false);