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

["Deng, Emily" <Emily.Deng@amd.com>]

[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@amd.com>
>Cc: dri-devel@lists.freedesktop.org; amd-gfx@lists.freedesktop.org; Koenig,
>Christian <Christian.Koenig@amd.com>; steven.price@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@amd.com>
>
>>-----Original Message-----
>>From: Grodzovsky, Andrey <Andrey.Grodzovsky@amd.com>
>>Sent: Tuesday, November 26, 2019 7:37 AM
>>Cc: dri-devel@lists.freedesktop.org; amd-gfx@lists.freedesktop.org;
>>Koenig, Christian <Christian.Koenig@amd.com>; Deng, Emily
>><Emily.Deng@amd.com>; steven.price@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@amd.com>
>>> Reviewed-by: Christian König <christian.koenig@amd.com>
>>> Tested-by: Emily Deng <Emily.Deng@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.
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