blocking ops in drm_sched_cleanup_jobs()
Koenig, Christian
Christian.Koenig at amd.com
Mon Sep 16 14:44:12 UTC 2019
Am 16.09.19 um 16:24 schrieb Daniel Vetter:
> On Mon, Sep 16, 2019 at 10:11 AM Koenig, Christian
> <Christian.Koenig at amd.com> wrote:
>> Hi Steven,
>>
>> the problem seems to be than panfrost is trying to sleep while freeing a
>> job. E.g. it tries to take a mutex.
>>
>> That is not allowed any more since we need to free the jobs from atomic
>> and even interrupt context.
>>
>> Your suggestion wouldn't work because this way jobs are not freed when
>> there isn't a new one to be scheduled.
> One fix would be to make sure that any that any calls to
> drm_sched_cleanup_jobs are atomic, by putting preempt_disable/enable
> or local_irq_disable/enable in there, at least when lockdep or sleep
> debugging is enabled. That should help catch these reliable, instead
> of just once every blue moon.
Yeah, thought about that as well. But I would also prefer a solution
where drm_sched_cleanup_jobs() is never called in an atomic context.
The problem is that I don't see how that can be possible without
delaying freeing of jobs.
Regards,
Christian.
> -Daniel
>
>> Regards,
>> Christian.
>>
>> Am 13.09.19 um 16:50 schrieb Steven Price:
>>> Hi,
>>>
>>> I hit the below splat randomly with panfrost. From what I can tell this
>>> is a more general issue which would affect other drivers.
>>>
>>> ----8<-----
>>> [58604.913130] ------------[ cut here ]------------
>>> [58604.918590] WARNING: CPU: 1 PID: 1758 at kernel/sched/core.c:6556 __might_sleep+0x74/0x98
>>> [58604.927965] do not call blocking ops when !TASK_RUNNING; state=1 set at [<0c590494>] prepare_to_wait_event+0x104/0x164
>>> [58604.940047] Modules linked in: panfrost gpu_sched
>>> [58604.945370] CPU: 1 PID: 1758 Comm: pan_js Not tainted 5.3.0-rc1+ #13
>>> [58604.952500] Hardware name: Rockchip (Device Tree)
>>> [58604.957815] [<c0111150>] (unwind_backtrace) from [<c010c99c>] (show_stack+0x10/0x14)
>>> [58604.966521] [<c010c99c>] (show_stack) from [<c07adbb4>] (dump_stack+0x9c/0xd4)
>>> [58604.974639] [<c07adbb4>] (dump_stack) from [<c0121da8>] (__warn+0xe8/0x104)
>>> [58604.982462] [<c0121da8>] (__warn) from [<c0121e08>] (warn_slowpath_fmt+0x44/0x6c)
>>> [58604.990867] [<c0121e08>] (warn_slowpath_fmt) from [<c014eccc>] (__might_sleep+0x74/0x98)
>>> [58604.999973] [<c014eccc>] (__might_sleep) from [<c07c73d8>] (__mutex_lock+0x38/0x948)
>>> [58605.008690] [<c07c73d8>] (__mutex_lock) from [<c07c7d00>] (mutex_lock_nested+0x18/0x20)
>>> [58605.017841] [<c07c7d00>] (mutex_lock_nested) from [<bf00b54c>] (panfrost_gem_free_object+0x60/0x10c [panfrost])
>>> [58605.029430] [<bf00b54c>] (panfrost_gem_free_object [panfrost]) from [<bf00cecc>] (panfrost_job_put+0x138/0x150 [panfrost])
>>> [58605.042076] [<bf00cecc>] (panfrost_job_put [panfrost]) from [<bf00121c>] (drm_sched_cleanup_jobs+0xc8/0xe0 [gpu_sched])
>>> [58605.054417] [<bf00121c>] (drm_sched_cleanup_jobs [gpu_sched]) from [<bf001300>] (drm_sched_main+0xcc/0x26c [gpu_sched])
>>> [58605.066620] [<bf001300>] (drm_sched_main [gpu_sched]) from [<c0146cfc>] (kthread+0x13c/0x154)
>>> [58605.076226] [<c0146cfc>] (kthread) from [<c01010b4>] (ret_from_fork+0x14/0x20)
>>> [58605.084346] Exception stack(0xe959bfb0 to 0xe959bff8)
>>> [58605.090046] bfa0: 00000000 00000000 00000000 00000000
>>> [58605.099250] bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>>> [58605.108480] bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
>>> [58605.116210] irq event stamp: 179
>>> [58605.119955] hardirqs last enabled at (187): [<c017f7e4>] console_unlock+0x564/0x5c4
>>> [58605.128935] hardirqs last disabled at (202): [<c017f308>] console_unlock+0x88/0x5c4
>>> [58605.137788] softirqs last enabled at (216): [<c0102334>] __do_softirq+0x18c/0x548
>>> [58605.146543] softirqs last disabled at (227): [<c0129528>] irq_exit+0xc4/0x10c
>>> [58605.154618] ---[ end trace f65bdbd9ea9adfc0 ]---
>>> ----8<-----
>>>
>>> The problem is that drm_sched_main() calls drm_sched_cleanup_jobs() as
>>> part of the condition of wait_event_interruptible:
>>>
>>>> wait_event_interruptible(sched->wake_up_worker,
>>>> (drm_sched_cleanup_jobs(sched),
>>>> (!drm_sched_blocked(sched) &&
>>>> (entity = drm_sched_select_entity(sched))) ||
>>>> kthread_should_stop()));
>>> When drm_sched_cleanup_jobs() is called *after* a wait (i.e. after
>>> prepare_to_wait_event() has been called), then any might_sleep() will
>>> moan loudly about it. This doesn't seem to happen often (I've only
>>> triggered it once) because usually drm_sched_cleanup_jobs() either
>>> doesn't sleep or does the sleeping during the first call that
>>> wait_event_interruptible() makes (which is before the task state is set).
>>>
>>> I don't really understand why drm_sched_cleanup_jobs() needs to be
>>> called here, a simple change like below 'fixes' it. But I presume
>>> there's some reason for the call being part of the
>>> wait_event_interruptible condition. Can anyone shed light on this?
>>>
>>> The code was introduced in commit 5918045c4ed4 ("drm/scheduler: rework job destruction")
>>>
>>> Steve
>>>
>>> ----8<-----
>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>>> index 9a0ee74d82dc..528f295e3a31 100644
>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>> @@ -699,11 +699,12 @@ static int drm_sched_main(void *param)
>>> struct drm_sched_job *sched_job;
>>> struct dma_fence *fence;
>>>
>>> + drm_sched_cleanup_jobs(sched);
>>> +
>>> wait_event_interruptible(sched->wake_up_worker,
>>> - (drm_sched_cleanup_jobs(sched),
>>> (!drm_sched_blocked(sched) &&
>>> (entity = drm_sched_select_entity(sched))) ||
>>> - kthread_should_stop()));
>>> + kthread_should_stop());
>>>
>>> if (!entity)
>>> continue;
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