Re: [PATCH] sched/rt/deadline: Don't push if task's scheduling class was changed

[Steven Rostedt <rostedt@goodmis.org>]

On Mon,  9 May 2016 12:11:31 +0800
Xunlei Pang <xlpang@redhat.com> wrote:

> We got a warning below:
>     WARNING: CPU: 1 PID: 2468 at kernel/sched/core.c:1161 set_task_cpu+0x1af/0x1c0
>     CPU: 1 PID: 2468 Comm: bugon Not tainted 4.6.0-rc3+ #16
>     Hardware name: Intel Corporation Broadwell Client
>     0000000000000086 0000000089618374 ffff8800897a7d50 ffffffff8133dc8c
>     0000000000000000 0000000000000000 ffff8800897a7d90 ffffffff81089921
>     0000048981037f39 ffff88016c4315c0 ffff88016ecd6e40 0000000000000000
>     Call Trace:
>     [<ffffffff8133dc8c>] dump_stack+0x63/0x87
>     [<ffffffff81089921>] __warn+0xd1/0xf0
>     [<ffffffff81089a5d>] warn_slowpath_null+0x1d/0x20
>     [<ffffffff810b48ff>] set_task_cpu+0x1af/0x1c0
>     [<ffffffff810cc90a>] push_dl_task.part.34+0xea/0x180
>     [<ffffffff810ccd17>] push_dl_tasks+0x17/0x30
>     [<ffffffff8118d17a>] __balance_callback+0x45/0x5c
>     [<ffffffff810b2f46>] __sched_setscheduler+0x906/0xb90
>     [<ffffffff810b6f50>] SyS_sched_setattr+0x150/0x190
>     [<ffffffff81003c12>] do_syscall_64+0x62/0x110
>     [<ffffffff816b5021>] entry_SYSCALL64_slow_path+0x25/0x25
> 
> The corresponding warning triggering code:
>     WARN_ON_ONCE(p->state == TASK_RUNNING &&
>              p->sched_class == &fair_sched_class &&
>              (p->on_rq && !task_on_rq_migrating(p)))
> 
> This is because in find_lock_later_rq(), the task whose scheduling
> class was changed to fair class is still pushed away as deadline.
> 
> So, check in find_lock_later_rq() after double_lock_balance(), if the
> scheduling class of the deadline task was changed, break and retry.
> Apply the same logic to RT.
> 
> Signed-off-by: Xunlei Pang <xlpang@redhat.com>

Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve


> ---
>  kernel/sched/deadline.c | 1 +
>  kernel/sched/rt.c       | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 169d40d..57eb3e4 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1385,6 +1385,7 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
>  				     !cpumask_test_cpu(later_rq->cpu,
>  				                       &task->cpus_allowed) ||
>  				     task_running(rq, task) ||
> +				     !dl_task(task) ||
>  				     !task_on_rq_queued(task))) {
>  				double_unlock_balance(rq, later_rq);
>  				later_rq = NULL;
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index ecfc83d..c10a6f5 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1720,6 +1720,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
>  				     !cpumask_test_cpu(lowest_rq->cpu,
>  						       tsk_cpus_allowed(task)) ||
>  				     task_running(rq, task) ||
> +				     !rt_task(task) ||
>  				     !task_on_rq_queued(task))) {
>  
>  				double_unlock_balance(rq, lowest_rq);