Tested-by: Emily Deng <Emily.Deng@xxxxxxx>
>-----Original Message-----
>From: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
>Sent: Tuesday, November 19, 2019 1:52 AM
>Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx; amd-gfx@xxxxxxxxxxxxxxxxxxxxx; Koenig,
>Christian <Christian.Koenig@xxxxxxx>; Deng, Emily
><Emily.Deng@xxxxxxx>; Grodzovsky, Andrey
><Andrey.Grodzovsky@xxxxxxx>
>Subject: [PATCH v2] drm/scheduler: Avoid accessing freed bad job.
>
>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.
>
>Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
>---
> drivers/gpu/drm/scheduler/sched_main.c | 44
>+++++++++++++++++++++++++++++-----
> 1 file changed, 38 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/gpu/drm/scheduler/sched_main.c
>b/drivers/gpu/drm/scheduler/sched_main.c
>index 80ddbdf..b05b210 100644
>--- a/drivers/gpu/drm/scheduler/sched_main.c
>+++ b/drivers/gpu/drm/scheduler/sched_main.c
>@@ -287,10 +287,24 @@ 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_cleanup_jobs
>that
>+ * is already in progress.
>+ */
>+ 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 already in
>progress
>+ * drm_sched_cleanup_jobs. It will be reinsrted 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);
>
> /*
>@@ -302,6 +316,8 @@ static void drm_sched_job_timedout(struct
>work_struct *work)
> sched->free_guilty = false;
> }
> }
>+ else
>+ spin_unlock_irqrestore(&sched->job_list_lock, flags);
>
> spin_lock_irqsave(&sched->job_list_lock, flags);
> drm_sched_start_timeout(sched);
>@@ -373,6 +389,19 @@ 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_cleanup_jobs
>+ * cannot race against us and release the bad job at this point - we
>parked
>+ * (waited for) any in progress (earlier) cleanups and any later ones will
>+ * bail out due to sched->thread being parked.
>+ */
>+ 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.
>@@ -656,16 +685,19 @@ static void drm_sched_cleanup_jobs(struct
>drm_gpu_scheduler *sched)
> __kthread_should_park(sched->thread))
> return;
>
>-
>- while (!list_empty(&sched->ring_mirror_list)) {
>+ /* See drm_sched_job_timedout for why the locking is here */
>+ while (true) {
> struct drm_sched_job *job;
>
>- job = list_first_entry(&sched->ring_mirror_list,
>- struct drm_sched_job, node);
>- if (!dma_fence_is_signaled(&job->s_fence->finished))
>+ 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 || !dma_fence_is_signaled(&job->s_fence->finished)) {
>+ spin_unlock_irqrestore(&sched->job_list_lock, flags);
> break;
>+ }
>
>- spin_lock_irqsave(&sched->job_list_lock, flags);
> /* remove job from ring_mirror_list */
> list_del_init(&job->node);
> spin_unlock_irqrestore(&sched->job_list_lock, flags);
>--
>2.7.4
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