Messages in this thread Patch in this message | | | From | Li Bin <> | Subject | [PATCH 2/2] sched/deadline.c: pick and check task if double_lock_balance() unlock the rq | Date | Thu, 12 Apr 2018 18:58:55 +0800 |
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push_dl_task() pick the first pushable task and find an eligible later_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.libin@huawei.com> --- kernel/sched/deadline.c | 48 +++++++++++++++++++++++------------------------- 1 file changed, 23 insertions(+), 25 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 9df0978..87cd7ca 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 +1985,9 @@ 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 = 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 +2012,6 @@ 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
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