sched/deadline: Stop dl_server before CPU goes offline

IBM CI tool reported kernel warning[1] when running a CPU removal
operation through drmgr[2]. i.e "drmgr -c cpu -r -q 1"

WARNING: CPU: 0 PID: 0 at kernel/sched/cpudeadline.c:219 cpudl_set+0x58/0x170
NIP [c0000000002b6ed8] cpudl_set+0x58/0x170
LR [c0000000002b7cb8] dl_server_timer+0x168/0x2a0
Call Trace:
[c000000002c2f8c0] init_stack+0x78c0/0x8000 (unreliable)
[c0000000002b7cb8] dl_server_timer+0x168/0x2a0
[c00000000034df84] __hrtimer_run_queues+0x1a4/0x390
[c00000000034f624] hrtimer_interrupt+0x124/0x300
[c00000000002a230] timer_interrupt+0x140/0x320

Git bisects to: commit 4ae8d9aa9f9d ("sched/deadline: Fix dl_server getting stuck")

This happens since:
- dl_server hrtimer gets enqueued close to cpu offline, when
  kthread_park enqueues a fair task.
- CPU goes offline and drmgr removes it from cpu_present_mask.
- hrtimer fires and warning is hit.

Fix it by stopping the dl_server before CPU is marked dead.

[1]: https://lore.kernel.org/all/8218e149-7718-4432-9312-f97297c352b9@linux.ibm.com/
[2]: https://github.com/ibm-power-utilities/powerpc-utils/tree/next/src/drmgr

[sshegde: wrote the changelog and tested it]
Fixes: 4ae8d9aa9f9d ("sched/deadline: Fix dl_server getting stuck")
Closes: https://lore.kernel.org/all/8218e149-7718-4432-9312-f97297c352b9@linux.ibm.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 198d2dd45f59cbcc0e6e7689eb7a9811969241d0..f1ebf67b48e2116202bc84b63bef2f9c79a376bc 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8571,10 +8571,12 @@ int sched_cpu_dying(unsigned int cpu)
        sched_tick_stop(cpu);
 
        rq_lock_irqsave(rq, &rf);
+       update_rq_clock(rq);
        if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) {
                WARN(true, "Dying CPU not properly vacated!");
                dump_rq_tasks(rq, KERN_WARNING);
        }
+       dl_server_stop(&rq->fair_server);
        rq_unlock_irqrestore(rq, &rf);
 
        calc_load_migrate(rq);

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 615411a0a8813d44d817bfef6aee945437e362f1..7b7671060bf9ed51312edfba2cf130f44de8c39b 100644 (file)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1582,6 +1582,9 @@ void dl_server_start(struct sched_dl_entity *dl_se)
        if (!dl_server(dl_se) || dl_se->dl_server_active)
                return;
 
+       if (WARN_ON_ONCE(!cpu_online(cpu_of(rq))))
+               return;
+
        dl_se->dl_server_active = 1;
        enqueue_dl_entity(dl_se, ENQUEUE_WAKEUP);
        if (!dl_task(dl_se->rq->curr) || dl_entity_preempt(dl_se, &rq->curr->dl))