[PATCH 3/3] sched_ext: Use rcu_access_pointer() for the first_task comparison

[Tejun Heo]

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.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 kernel/sched/ext/ext.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 95aadce7b104..53e4aaac46b7 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -1642,7 +1642,7 @@ static void task_unlink_from_dsq(struct task_struct *p,
 	list_del_init(&p->scx.dsq_list.node);
 	dsq_dec_nr(dsq, p);
 
-	if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN) && dsq->first_task == p) {
+	if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN) && rcu_access_pointer(dsq->first_task) == p) {
 		struct task_struct *first_task;
 
 		first_task = nldsq_next_task(dsq, NULL, false);
-- 
2.55.0