Re: [PATCH] drm/amdgpu: Fix the null pointer issue for tdr

["Koenig, Christian" <Christian.Koenig-5C7GfCeVMHo@public.gmane.org>]

Am 08.11.19 um 09:52 schrieb Deng, Emily:
> Ping.....

You need to give me at least enough time to wake up :)

>
>
> Best wishes
> Emily Deng
>
>
>
>> -----Original Message-----
>> From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of Deng,
>> Emily
>> Sent: Friday, November 8, 2019 10:56 AM
>> To: Koenig, Christian <Christian.Koenig@amd.com>; amd-
>> gfx@lists.freedesktop.org
>> Subject: RE: [PATCH] drm/amdgpu: Fix the null pointer issue for tdr
>>
>>> -----Original Message-----
>>> From: Christian König <ckoenig.leichtzumerken@gmail.com>
>>> Sent: Thursday, November 7, 2019 7:28 PM
>>> To: Deng, Emily <Emily.Deng@amd.com>; amd-gfx@lists.freedesktop.org
>>> Subject: Re: [PATCH] drm/amdgpu: Fix the null pointer issue for tdr
>>>
>>> Am 07.11.19 um 11:25 schrieb Emily Deng:
>>>> When the job is already signaled, the s_fence is freed. Then it will
>>>> has null pointer in amdgpu_device_gpu_recover.
>>> NAK, the s_fence is only set to NULL when the job is destroyed. See
>>> drm_sched_job_cleanup().
>> I know it is set to NULL in drm_sched_job_cleanup. But in one case, when it
>> enter into the amdgpu_device_gpu_recover, it already in
>> drm_sched_job_cleanup, and at this time, it will go to free job. But the
>> amdgpu_device_gpu_recover sometimes is faster. At that time, job is not
>> freed, but s_fence is already NULL.

No, that case can't happen. See here:

>         drm_sched_job_cleanup(s_job);
>
>         amdgpu_ring_priority_put(ring, s_job->s_priority);
>         dma_fence_put(job->fence);
>         amdgpu_sync_free(&job->sync);
>         amdgpu_sync_free(&job->sched_sync);
>         kfree(job);

The job itself is freed up directly after freeing the reference to the 
s_fence.

So you are just papering over a much bigger problem here. This patch is 
a clear NAK.

Regards,
Christian.

>>> When you see a job without an s_fence then that means the problem is
>>> somewhere else.
>>>
>>> Regards,
>>> Christian.
>>>
>>>> Signed-off-by: Emily Deng <Emily.Deng@amd.com>
>>>> ---
>>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_device.c |  2 +-
>>>>    drivers/gpu/drm/scheduler/sched_main.c     | 11 ++++++-----
>>>>    2 files changed, 7 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> index e6ce949..5a8f08e 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> @@ -4075,7 +4075,7 @@ int amdgpu_device_gpu_recover(struct
>>> amdgpu_device *adev,
>>>>    	 *
>>>>    	 * job->base holds a reference to parent fence
>>>>    	 */
>>>> -	if (job && job->base.s_fence->parent &&
>>>> +	if (job && job->base.s_fence && job->base.s_fence->parent &&
>>>>    	    dma_fence_is_signaled(job->base.s_fence->parent))
>>>>    		job_signaled = true;
>>>>
>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c
>>>> b/drivers/gpu/drm/scheduler/sched_main.c
>>>> index 31809ca..56cc10e 100644
>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>> @@ -334,8 +334,8 @@ void drm_sched_increase_karma(struct
>>> drm_sched_job
>>>> *bad)
>>>>
>>>>    			spin_lock(&rq->lock);
>>>>    			list_for_each_entry_safe(entity, tmp, &rq->entities,
>>> list) {
>>>> -				if (bad->s_fence->scheduled.context ==
>>>> -				    entity->fence_context) {
>>>> +				if (bad->s_fence && (bad->s_fence-
>>>> scheduled.context ==
>>>> +				    entity->fence_context)) {
>>>>    					if (atomic_read(&bad->karma) >
>>>>    					    bad->sched->hang_limit)
>>>>    						if (entity->guilty)
>>>> @@ -376,7 +376,7 @@ void drm_sched_stop(struct drm_gpu_scheduler
>>> *sched, struct drm_sched_job *bad)
>>>>    	 * This iteration is thread safe as sched thread is stopped.
>>>>    	 */
>>>>    	list_for_each_entry_safe_reverse(s_job, tmp, &sched-
>>>> ring_mirror_list, node) {
>>>> -		if (s_job->s_fence->parent &&
>>>> +		if (s_job->s_fence && s_job->s_fence->parent &&
>>>>    		    dma_fence_remove_callback(s_job->s_fence->parent,
>>>>    					      &s_job->cb)) {
>>>>    			atomic_dec(&sched->hw_rq_count); @@ -395,7
>> +395,8 @@ void
>>>> drm_sched_stop(struct drm_gpu_scheduler
>>> *sched, struct drm_sched_job *bad)
>>>>    			 *
>>>>    			 * Job is still alive so fence refcount at least 1
>>>>    			 */
>>>> -			dma_fence_wait(&s_job->s_fence->finished, false);
>>>> +			if (s_job->s_fence)
>>>> +				dma_fence_wait(&s_job->s_fence->finished,
>>> false);
>>>>    			/*
>>>>    			 * We must keep bad job alive for later use during @@
>>> -438,7
>>>> +439,7 @@ void drm_sched_start(struct drm_gpu_scheduler *sched, bool
>>> full_recovery)
>>>>    	 * GPU recovers can't run in parallel.
>>>>    	 */
>>>>    	list_for_each_entry_safe(s_job, tmp, &sched->ring_mirror_list,
>>>> node)
>>> {
>>>> -		struct dma_fence *fence = s_job->s_fence->parent;
>>>> +		struct dma_fence *fence = s_job->s_fence ? s_job->s_fence-
>>>> parent :
>>>> +NULL;
>>>>
>>>>    		atomic_inc(&sched->hw_rq_count);
>>>>
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