From: Peter Zijlstra Date: Fri, 30 Jan 2026 12:41:00 +0000 (+0100) Subject: sched/deadline: Fix 'stuck' dl_server X-Git-Tag: v6.19-rc8~3^2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=115135422562e2f791e98a6f55ec57b2da3b3a95;p=thirdparty%2Flinux.git sched/deadline: Fix 'stuck' dl_server Andrea reported the dl_server getting stuck for him. He tracked it down to a state where dl_server_start() saw dl_defer_running==1, but the dl_server's job is no longer valid at the time of dl_server_start(). In the state diagram this corresponds to [4] D->A (or dl_server_stop() due to no more runnable tasks) followed by [1], which in case of a lapsed deadline must then be A->B. Now our A has dl_defer_running==1, while B demands dl_defer_running==0, therefore it must get cleared when the CBS wakeup rules demand a replenish. Fixes: a110a81c52a9 ("sched/deadline: Deferrable dl server") Reported-by: Andrea Righi arighi@nvidia.com Signed-off-by: Peter Zijlstra (Intel) Acked-by: Juri Lelli Tested-by: Andrea Righi arighi@nvidia.com Link: https://lkml.kernel.org/r/20260123161645.2181752-1-arighi@nvidia.com Link: https://patch.msgid.link/20260130124100.GC1079264@noisy.programming.kicks-ass.net --- diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index c509f2e7d69d..7bcde7114f1b 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1034,6 +1034,12 @@ static void update_dl_entity(struct sched_dl_entity *dl_se) return; } + /* + * When [4] D->A is followed by [1] A->B, dl_defer_running + * needs to be cleared, otherwise it will fail to properly + * start the zero-laxity timer. + */ + dl_se->dl_defer_running = 0; replenish_dl_new_period(dl_se, rq); } else if (dl_server(dl_se) && dl_se->dl_defer) { /* @@ -1655,6 +1661,12 @@ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec) * dl_server_active = 1; * enqueue_dl_entity() * update_dl_entity(WAKEUP) + * if (dl_time_before() || dl_entity_overflow()) + * dl_defer_running = 0; + * replenish_dl_new_period(); + * // fwd period + * dl_throttled = 1; + * dl_defer_armed = 1; * if (!dl_defer_running) * dl_defer_armed = 1; * dl_throttled = 1;