diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2026-01-30 13:41:00 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-01-30 23:06:06 +0100 |
| commit | 115135422562e2f791e98a6f55ec57b2da3b3a95 (patch) | |
| tree | 301a1a40cda10531e3d4b518e8e8bdc0dde0ca34 | |
| parent | 63804fed149a6750ffd28610c5c1c98cce6bd377 (diff) | |
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the dl_server's job is no longer valid at the time of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) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
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
| -rw-r--r-- | kernel/sched/deadline.c | 12 |
1 files changed, 12 insertions, 0 deletions
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; |