push_dl_task() pick the first pushable task and find an eligible
lowest_rq, then double_lock_balance(rq, lowest_rq). So if
double_lock_balance() unlock the rq (when double_lock_balance() return
1), we have to check if this task is still on the rq.
The problem is that the check conditions are not sufficient:
if (unlikely(task_rq(task) != rq ||
!cpumask_test_cpu(later_rq->cpu, &task->cpus_allowed) ||
task_running(rq, task) ||
!dl_task(task) ||
!task_on_rq_queued(task))) {
cpu2 cpu1 cpu0
push_dl_task(rq1)
pick task_A on rq1
find rq0
double_lock_balance(rq1, rq0)
unlock(rq1)
rq1 __schedule
pick task_A run
task_A sleep (dequeued)
lock(rq0)
lock(rq1)
do_above_check(task_A)
task_rq(task_A) == rq1
cpus_allowed unchanged
task_running == false
dl_task(task_A) == true
try_to_wake_up(task_A)
select_cpu = cpu3
enqueue(rq3, task_A)
task_A->on_rq = 1
task_on_rq_queued(task_A)
above_check passed, return rq0
...
migrate task_A from rq1 to rq0
So we can't rely on these checks of task_A to make sure the task_A is
still on the rq1, even though we hold the rq1->lock. This patch will
repick the first pushable task to be sure the task is still on the rq.
Signed-off-by: Li Bin <huawei.li...@huawei.com>
Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rost...@goodmis.org>
---
kernel/sched/deadline.c | 55 +++++++++++++++++++++++++++----------------------
1 file changed, 30 insertions(+), 25 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 9df0978..8e0f6a4 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1936,6 +1936,26 @@ static int find_later_rq(struct task_struct *task)
return -1;
}
+static struct task_struct *pick_next_pushable_dl_task(struct rq *rq)
+{
+ struct task_struct *p;
+
+ if (!has_pushable_dl_tasks(rq))
+ return NULL;
+
+ p = rb_entry(rq->dl.pushable_dl_tasks_root.rb_leftmost,
+ struct task_struct, pushable_dl_tasks);
+
+ BUG_ON(rq->cpu != task_cpu(p));
+ BUG_ON(task_current(rq, p));
+ BUG_ON(p->nr_cpus_allowed <= 1);
+
+ BUG_ON(!task_on_rq_queued(p));
+ BUG_ON(!dl_task(p));
+
+ return p;
+}
+
/* Locks the rq it finds */
static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
{
@@ -1965,11 +1985,16 @@ static struct rq *find_lock_later_rq(struct task_struct
*task, struct rq *rq)
/* Retry if something changed. */
if (double_lock_balance(rq, later_rq)) {
- if (unlikely(task_rq(task) != rq ||
- !cpumask_test_cpu(later_rq->cpu,
&task->cpus_allowed) ||
- task_running(rq, task) ||
- !dl_task(task) ||
- !task_on_rq_queued(task))) {
+ struct task_struct *next_task;
+ /*
+ * We had to unlock the run queue. In
+ * the mean time, task could have
+ * migrated already or had its affinity changed.
+ * Also make sure that it wasn't scheduled on its rq.
+ */
+ next_task = pick_next_pushable_dl_task(rq);
+ if (unlikely(next_task != task ||
+
!cpumask_test_cpu(later_rq->cpu, &task->cpus_allowed))) {
double_unlock_balance(rq, later_rq);
later_rq = NULL;
break;
@@ -1994,26 +2019,6 @@ static struct rq *find_lock_later_rq(struct task_struct
*task, struct rq *rq)
return later_rq;
}
-static struct task_struct *pick_next_pushable_dl_task(struct rq *rq)
-{
- struct task_struct *p;
-
- if (!has_pushable_dl_tasks(rq))
- return NULL;
-
- p = rb_entry(rq->dl.pushable_dl_tasks_root.rb_leftmost,
- struct task_struct, pushable_dl_tasks);
-
- BUG_ON(rq->cpu != task_cpu(p));
- BUG_ON(task_current(rq, p));
- BUG_ON(p->nr_cpus_allowed <= 1);
-
- BUG_ON(!task_on_rq_queued(p));
- BUG_ON(!dl_task(p));
-
- return p;
-}
-
/*
* See if the non running -deadline tasks on this rq
* can be sent to some other CPU where they can preempt
--
1.7.12.4
