[PATCH 03/11] Do not initialize the deadline timer if it is already initialized

[Luca Abeni]

After commit 67dfa1b756f250972bde31d65e3f8fde6aeddc5b changing the
parameters of a SCHED_DEADLINE tasks might crash the system. This
happens because 67dfa1b756f250972bde31d65e3f8fde6aeddc5b removed the
following lines from init_dl_task_timer():
-       if (hrtimer_active(timer)) {
-               hrtimer_try_to_cancel(timer);
-               return;
-       }

As a result, if sched_setattr() is invoked to change the parameters
(runtime or period) of a SCHED_DEADLINE task, init_dl_task_timer()
might end up initializing a pending timer.

Fix this problem by modifying __setparam_dl() to call init_dl_task_timer()
only if the task is not already a SCHED_DEADLINE one.
---
 kernel/sched/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b5797b7..470111c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3251,7 +3251,9 @@ __setparam_dl(struct task_struct *p, const struct sched_attr *attr)
 {
 	struct sched_dl_entity *dl_se = &p->dl;
 
-	init_dl_task_timer(dl_se);
+        if (p->sched_class != &dl_sched_class) {
+		init_dl_task_timer(dl_se);
+	}
 	dl_se->dl_runtime = attr->sched_runtime;
 	dl_se->dl_deadline = attr->sched_deadline;
 	dl_se->dl_period = attr->sched_period ?: dl_se->dl_deadline;
-- 
2.1.0


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