linux-kernel - Re: drm_sched with panfrost crash on T820

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Date:   Fri, 4 Oct 2019 17:03:15 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     "Grodzovsky, Andrey" <Andrey.Grodzovsky@....com>,
        Hillf Danton <hdanton@...a.com>
Cc:     "daniel@...ll.ch" <daniel@...ll.ch>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        Erico Nunes <nunes.erico@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "steven.price@....com" <steven.price@....com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>
Subject: Re: drm_sched with panfrost crash on T820

On 04/10/2019 16:53, Grodzovsky, Andrey wrote:
> 
> On 10/3/19 4:34 AM, Neil Armstrong wrote:
>> Hi Andrey,
>>
>> Le 02/10/2019 à 16:40, Grodzovsky, Andrey a écrit :
>>> On 9/30/19 10:52 AM, Hillf Danton wrote:
>>>> On Mon, 30 Sep 2019 11:17:45 +0200 Neil Armstrong wrote:
>>>>> Did a new run from 5.3:
>>>>>
>>>>> [   35.971972] Call trace:
>>>>> [   35.974391]  drm_sched_increase_karma+0x5c/0xf0
>>>>> 			ffff000010667f38	FFFF000010667F94
>>>>> 			drivers/gpu/drm/scheduler/sched_main.c:335
>>>>>
>>>>> The crashing line is :
>>>>>                                   if (bad->s_fence->scheduled.context ==
>>>>>                                       entity->fence_context) {
>>>>>
>>>>> Doesn't seem related to guilty job.
>>>> Bail out if s_fence is no longer fresh.
>>>>
>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>> @@ -333,6 +333,10 @@ void drm_sched_increase_karma(struct drm
>>>>    
>>>>    			spin_lock(&rq->lock);
>>>>    			list_for_each_entry_safe(entity, tmp, &rq->entities, list) {
>>>> +				if (!smp_load_acquire(&bad->s_fence)) {
>>>> +					spin_unlock(&rq->lock);
>>>> +					return;
>>>> +				}
>>>>    				if (bad->s_fence->scheduled.context ==
>>>>    				    entity->fence_context) {
>>>>    					if (atomic_read(&bad->karma) >
>>>> @@ -543,7 +547,7 @@ EXPORT_SYMBOL(drm_sched_job_init);
>>>>    void drm_sched_job_cleanup(struct drm_sched_job *job)
>>>>    {
>>>>    	dma_fence_put(&job->s_fence->finished);
>>>> -	job->s_fence = NULL;
>>>> +	smp_store_release(&job->s_fence, 0);
>>>>    }
>>>>    EXPORT_SYMBOL(drm_sched_job_cleanup);
>> This fixed the problem on the 10 CI runs.
>>
>> Neil
> 
> 
> These are good news but I still fail to see how this fixes the problem - 
> Hillf, do you mind explaining how you came up with this particular fix - 
> what was the bug you saw ?

As Steven explained, seems the same job was submitted on both HW slots,
and then when timeout occurs each thread calls panfrost_job_timedout
which leads to drm_sched_stop() on the first call and on the
second call the job was already freed.

Steven proposed a working fix, and this one does the same but on
the drm_sched side. This one looks cleaner, but panfrost should
not call drm_sched_stop() twice for the same job.

Neil

> 
> Andrey
> 
>>
>>> Does this change help the problem ? Note that drm_sched_job_cleanup is
>>> called from scheduler thread which is stopped at all times when work_tdr
>>> thread is running and anyway the 'bad' job is still in the
>>> ring_mirror_list while it's being accessed from
>>> drm_sched_increase_karma so I don't think drm_sched_job_cleanup can be
>>> called for it BEFORE or while drm_sched_increase_karma is executed.
>>>
>>> Andrey
>>>
>>>
>>>>    
>>>> --
>>>>