[PATCH] drm/xe: Limit number of jobs per exec queue

[Shuicheng Lin <shuicheng.lin@intel.com>]

Add a limit to the number of jobs that can be queued in a single
exec queue to avoid potential resource exhaustion.

A new field `job_cnt` is introduced in `struct xe_exec_queue` to
track the number of active DRM jobs, along with a maximum limit
`XE_MAX_JOB_COUNT_PER_EXEC_QUEUE` set to 0x1000.

If the job count exceeds this threshold, `xe_exec_ioctl()` now
returns `-EAGAIN` to signal that the caller should retry later.

Suggested-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
---
 drivers/gpu/drm/xe/xe_exec.c             | 5 +++++
 drivers/gpu/drm/xe/xe_exec_queue_types.h | 5 +++++
 drivers/gpu/drm/xe/xe_sched_job.c        | 2 ++
 3 files changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_exec.c b/drivers/gpu/drm/xe/xe_exec.c
index 0dc27476832b..722a5ac0200a 100644
--- a/drivers/gpu/drm/xe/xe_exec.c
+++ b/drivers/gpu/drm/xe/xe_exec.c
@@ -154,6 +154,11 @@ int xe_exec_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 		goto err_exec_queue;
 	}
 
+	if (q->job_cnt >= XE_MAX_JOB_COUNT_PER_EXEC_QUEUE) {
+		err = -EAGAIN;
+		goto err_exec_queue;
+	}
+
 	if (args->num_syncs) {
 		syncs = kcalloc(args->num_syncs, sizeof(*syncs), GFP_KERNEL);
 		if (!syncs) {
diff --git a/drivers/gpu/drm/xe/xe_exec_queue_types.h b/drivers/gpu/drm/xe/xe_exec_queue_types.h
index 282505fa1377..5f3219acec3c 100644
--- a/drivers/gpu/drm/xe/xe_exec_queue_types.h
+++ b/drivers/gpu/drm/xe/xe_exec_queue_types.h
@@ -162,6 +162,11 @@ struct xe_exec_queue {
 	const struct xe_ring_ops *ring_ops;
 	/** @entity: DRM sched entity for this exec queue (1 to 1 relationship) */
 	struct drm_sched_entity *entity;
+
+#define XE_MAX_JOB_COUNT_PER_EXEC_QUEUE	0x1000
+
+	/** @job_cnt: number of drm jobs in this exec queue */
+	u32 job_cnt;
 	/**
 	 * @tlb_flush_seqno: The seqno of the last rebind tlb flush performed
 	 * Protected by @vm's resv. Unused if @vm == NULL.
diff --git a/drivers/gpu/drm/xe/xe_sched_job.c b/drivers/gpu/drm/xe/xe_sched_job.c
index d21bf8f26964..37f58be7cbcc 100644
--- a/drivers/gpu/drm/xe/xe_sched_job.c
+++ b/drivers/gpu/drm/xe/xe_sched_job.c
@@ -146,6 +146,7 @@ struct xe_sched_job *xe_sched_job_create(struct xe_exec_queue *q,
 	for (i = 0; i < width; ++i)
 		job->ptrs[i].batch_addr = batch_addr[i];
 
+	q->job_cnt++;
 	xe_pm_runtime_get_noresume(job_to_xe(job));
 	trace_xe_sched_job_create(job);
 	return job;
@@ -177,6 +178,7 @@ void xe_sched_job_destroy(struct kref *ref)
 	dma_fence_put(job->fence);
 	drm_sched_job_cleanup(&job->drm);
 	job_free(job);
+	q->job_cnt--;
 	xe_exec_queue_put(q);
 	xe_pm_runtime_put(xe);
 }
-- 
2.49.0