[PATCH v4] drm/scheduler: Avoid accessing freed bad job.

[Andrey Grodzovsky]

Yes - Christian just pushed it to drm-next-misc - I guess Alex/Christian 
didn't pull to amd-staging-drm-next yet.

Andrey

On 12/2/19 2:24 PM, Deng, Emily wrote:
> [AMD Official Use Only - Internal Distribution Only]
>
> Hi Andrey,
>      Seems this patch is still not in amd-staging-drm-next?
>
> Best wishes
> Emily Deng
>
>
>
>> -----Original Message-----
>> From: Deng, Emily
>> Sent: Tuesday, November 26, 2019 4:41 PM
>> To: Grodzovsky, Andrey <Andrey.Grodzovsky at amd.com>
>> Cc: dri-devel at lists.freedesktop.org; amd-gfx at lists.freedesktop.org; Koenig,
>> Christian <Christian.Koenig at amd.com>; steven.price at arm.com
>> Subject: RE: [PATCH v4] drm/scheduler: Avoid accessing freed bad job.
>>
>> [AMD Official Use Only - Internal Distribution Only]
>>
>> Reviewed-by: Emily Deng <Emily.Deng at amd.com>
>>
>>> -----Original Message-----
>>> From: Grodzovsky, Andrey <Andrey.Grodzovsky at amd.com>
>>> Sent: Tuesday, November 26, 2019 7:37 AM
>>> Cc: dri-devel at lists.freedesktop.org; amd-gfx at lists.freedesktop.org;
>>> Koenig, Christian <Christian.Koenig at amd.com>; Deng, Emily
>>> <Emily.Deng at amd.com>; steven.price at arm.com
>>> Subject: Re: [PATCH v4] drm/scheduler: Avoid accessing freed bad job.
>>>
>>> Ping
>>>
>>> Andrey
>>>
>>> On 11/25/19 3:51 PM, Andrey Grodzovsky wrote:
>>>> Problem:
>>>> Due to a race between drm_sched_cleanup_jobs in sched thread and
>>>> drm_sched_job_timedout in timeout work there is a possiblity that bad
>>>> job was already freed while still being accessed from the timeout
>>>> thread.
>>>>
>>>> Fix:
>>>> Instead of just peeking at the bad job in the mirror list remove it
>>>> from the list under lock and then put it back later when we are
>>>> garanteed no race with main sched thread is possible which is after
>>>> the thread is parked.
>>>>
>>>> v2: Lock around processing ring_mirror_list in drm_sched_cleanup_jobs.
>>>>
>>>> v3: Rebase on top of drm-misc-next. v2 is not needed anymore as
>>>> drm_sched_get_cleanup_job already has a lock there.
>>>>
>>>> v4: Fix comments to relfect latest code in drm-misc.
>>>>
>>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
>>>> Reviewed-by: Christian König <christian.koenig at amd.com>
>>>> Tested-by: Emily Deng <Emily.Deng at amd.com>
>>>> ---
>>>>    drivers/gpu/drm/scheduler/sched_main.c | 27
>>> +++++++++++++++++++++++++++
>>>>    1 file changed, 27 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c
>>>> b/drivers/gpu/drm/scheduler/sched_main.c
>>>> index 6774955..1bf9c40 100644
>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>> @@ -284,10 +284,21 @@ static void drm_sched_job_timedout(struct
>>> work_struct *work)
>>>>    	unsigned long flags;
>>>>
>>>>    	sched = container_of(work, struct drm_gpu_scheduler,
>>>> work_tdr.work);
>>>> +
>>>> +	/* Protects against concurrent deletion in
>>> drm_sched_get_cleanup_job */
>>>> +	spin_lock_irqsave(&sched->job_list_lock, flags);
>>>>    	job = list_first_entry_or_null(&sched->ring_mirror_list,
>>>>    				       struct drm_sched_job, node);
>>>>
>>>>    	if (job) {
>>>> +		/*
>>>> +		 * Remove the bad job so it cannot be freed by concurrent
>>>> +		 * drm_sched_cleanup_jobs. It will be reinserted back after
>>> sched->thread
>>>> +		 * is parked at which point it's safe.
>>>> +		 */
>>>> +		list_del_init(&job->node);
>>>> +		spin_unlock_irqrestore(&sched->job_list_lock, flags);
>>>> +
>>>>    		job->sched->ops->timedout_job(job);
>>>>
>>>>    		/*
>>>> @@ -298,6 +309,8 @@ static void drm_sched_job_timedout(struct
>>> work_struct *work)
>>>>    			job->sched->ops->free_job(job);
>>>>    			sched->free_guilty = false;
>>>>    		}
>>>> +	} else {
>>>> +		spin_unlock_irqrestore(&sched->job_list_lock, flags);
>>>>    	}
>>>>
>>>>    	spin_lock_irqsave(&sched->job_list_lock, flags); @@ -370,6 +383,20
>>>> @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct
>>> drm_sched_job *bad)
>>>>    	kthread_park(sched->thread);
>>>>
>>>>    	/*
>>>> +	 * Reinsert back the bad job here - now it's safe as
>>>> +	 * drm_sched_get_cleanup_job cannot race against us and release the
>>>> +	 * bad job at this point - we parked (waited for) any in progress
>>>> +	 * (earlier) cleanups and drm_sched_get_cleanup_job will not be
>>> called
>>>> +	 * now until the scheduler thread is unparked.
>>>> +	 */
>>>> +	if (bad && bad->sched == sched)
>>>> +		/*
>>>> +		 * Add at the head of the queue to reflect it was the earliest
>>>> +		 * job extracted.
>>>> +		 */
>>>> +		list_add(&bad->node, &sched->ring_mirror_list);
>>>> +
>>>> +	/*
>>>>    	 * Iterate the job list from later to  earlier one and either deactive
>>>>    	 * their HW callbacks or remove them from mirror list if they already
>>>>    	 * signaled.