sched/fair: Use cfs_rq->h_curr in distribute_cfs_runtime()

distribute_cfs_runtime() refreshes the rq clock and accounts elapsed
runtime with update_curr() before redistributing bandwidth, but gates
this on cfs_rq->curr. Since commit 85570f10a4 ("sched/eevdf: Move to
a single runqueue") cfs_rq->curr is only maintained on the root
cfs_rq, so for the cgroup cfs_rqs it walks, the check never fires and
the refresh is dead code.

Use cfs_rq->h_curr, the per-level current entity, restoring the
intended behaviour: only refresh when something is actually running at
the throttled level, i.e. within the deferred throttle window.
Without this, runtime consumed by a still-running task of the
throttled hierarchy is not docked before redistribution;
unthrottle_cfs_rq() catches up unconditionally since
commit 28ad542768 ("sched/fair: Call update_curr() before
unthrottling the hierarchy"), so this is not a correctness hole today,
but the refresh the check was written for is gone.

Fixes: 85570f10a4 ("sched/eevdf: Move to a single runqueue")
Signed-off-by: Wanwu Li <liwanwu@kylinos.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Aaron Lu <ziqianlu@bytedance.com>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20260831101141.391382-3-liwanwu@kylinos.cn

kernel/sched/fair.c

@@ -7192,7 +7192,7 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
 		if (!list_empty(&cfs_rq->throttled_csd_list))
 			continue;
 
-		if (cfs_rq->curr) {
+		if (cfs_rq->h_curr) {
 			update_rq_clock(rq);
 			update_curr(cfs_rq);
 		}