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

[Deng, Emily]

[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.