drm/xe: Don't initialize fences at xe_sched_job_create()

Pre-allocate but don't initialize fences at xe_sched_job_create(),
and initialize / arm them instead at xe_sched_job_arm(). This
makes it possible to move xe_sched_job_create() with its memory
allocation out of any lock that is required for fence
initialization, and that may not allow memory allocation under it.

Replaces the struct dma_fence_array for parallell jobs with a
struct dma_fence_chain, since the former doesn't allow
a split-up between allocation and initialization.

v2:
- Rebase.
- Don't always use the first lrc when initializing parallel
  lrc fences.
- Use dma_fence_chain_contained() to access the lrc fences.

v4:
- Add an assert that job->lrc_seqno == fence->seqno.
  (Matthew Brost)

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com> #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20240527135912.152156-4-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/xe/xe_exec_queue.c

@@ -96,11 +96,6 @@ static struct xe_exec_queue *__xe_exec_queue_alloc(struct xe_device *xe,
 		}
 	}
 
-	if (xe_exec_queue_is_parallel(q)) {
-		q->parallel.composite_fence_ctx = dma_fence_context_alloc(1);
-		q->parallel.composite_fence_seqno = 0;
-	}
-
 	return q;
 }
 

drivers/gpu/drm/xe/xe_exec_queue_types.h

@@ -103,16 +103,6 @@ struct xe_exec_queue {
 		struct xe_guc_exec_queue *guc;
 	};
 
-	/**
-	 * @parallel: parallel submission state
-	 */
-	struct {
-		/** @parallel.composite_fence_ctx: context composite fence */
-		u64 composite_fence_ctx;
-		/** @parallel.composite_fence_seqno: seqno for composite fence */
-		u32 composite_fence_seqno;
-	} parallel;
-
 	/** @sched_props: scheduling properties */
 	struct {
 		/** @sched_props.timeslice_us: timeslice period in micro-seconds */

drivers/gpu/drm/xe/xe_ring_ops.c

@@ -366,7 +366,7 @@ static void emit_migration_job_gen12(struct xe_sched_job *job,
 
 	dw[i++] = MI_ARB_ON_OFF | MI_ARB_DISABLE; /* Enabled again below */
 
-	i = emit_bb_start(job->batch_addr[0], BIT(8), dw, i);
+	i = emit_bb_start(job->ptrs[0].batch_addr, BIT(8), dw, i);
 
 	if (!IS_SRIOV_VF(gt_to_xe(job->q->gt))) {
 		/* XXX: Do we need this? Leaving for now. */
@@ -375,7 +375,7 @@ static void emit_migration_job_gen12(struct xe_sched_job *job,
 		dw[i++] = preparser_disable(false);
 	}
 
-	i = emit_bb_start(job->batch_addr[1], BIT(8), dw, i);
+	i = emit_bb_start(job->ptrs[1].batch_addr, BIT(8), dw, i);
 
 	dw[i++] = MI_FLUSH_DW | MI_INVALIDATE_TLB | job->migrate_flush_flags |
 		MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_IMM_DW;
@@ -397,7 +397,7 @@ static void emit_job_gen12_gsc(struct xe_sched_job *job)
 	xe_gt_assert(gt, job->q->width <= 1); /* no parallel submission for GSCCS */
 
 	__emit_job_gen12_simple(job, job->q->lrc,
-				job->batch_addr[0],
+				job->ptrs[0].batch_addr,
 				xe_sched_job_lrc_seqno(job));
 }
 
@@ -413,7 +413,7 @@ static void emit_job_gen12_copy(struct xe_sched_job *job)
 
 	for (i = 0; i < job->q->width; ++i)
 		__emit_job_gen12_simple(job, job->q->lrc + i,
-					job->batch_addr[i],
+					job->ptrs[i].batch_addr,
 					xe_sched_job_lrc_seqno(job));
 }
 
@@ -424,7 +424,7 @@ static void emit_job_gen12_video(struct xe_sched_job *job)
 	/* FIXME: Not doing parallel handshake for now */
 	for (i = 0; i < job->q->width; ++i)
 		__emit_job_gen12_video(job, job->q->lrc + i,
-				       job->batch_addr[i],
+				       job->ptrs[i].batch_addr,
 				       xe_sched_job_lrc_seqno(job));
 }
 
@@ -434,7 +434,7 @@ static void emit_job_gen12_render_compute(struct xe_sched_job *job)
 
 	for (i = 0; i < job->q->width; ++i)
 		__emit_job_gen12_render_compute(job, job->q->lrc + i,
-						job->batch_addr[i],
+						job->ptrs[i].batch_addr,
 						xe_sched_job_lrc_seqno(job));
 }
 

drivers/gpu/drm/xe/xe_sched_job.c

@@ -6,7 +6,7 @@
 #include "xe_sched_job.h"
 
 #include <drm/xe_drm.h>
-#include <linux/dma-fence-array.h>
+#include <linux/dma-fence-chain.h>
 #include <linux/slab.h>
 
 #include "xe_device.h"
@@ -29,15 +29,15 @@ int __init xe_sched_job_module_init(void)
 	xe_sched_job_slab =
 		kmem_cache_create("xe_sched_job",
 				  sizeof(struct xe_sched_job) +
-				  sizeof(u64), 0,
+				  sizeof(struct xe_job_ptrs), 0,
 				  SLAB_HWCACHE_ALIGN, NULL);
 	if (!xe_sched_job_slab)
 		return -ENOMEM;
 
 	xe_sched_job_parallel_slab =
 		kmem_cache_create("xe_sched_job_parallel",
 				  sizeof(struct xe_sched_job) +
-				  sizeof(u64) *
+				  sizeof(struct xe_job_ptrs) *
 				  XE_HW_ENGINE_MAX_INSTANCE, 0,
 				  SLAB_HWCACHE_ALIGN, NULL);
 	if (!xe_sched_job_parallel_slab) {
@@ -79,26 +79,33 @@ static struct xe_device *job_to_xe(struct xe_sched_job *job)
 	return gt_to_xe(job->q->gt);
 }
 
+/* Free unused pre-allocated fences */
+static void xe_sched_job_free_fences(struct xe_sched_job *job)
+{
+	int i;
+
+	for (i = 0; i < job->q->width; ++i) {
+		struct xe_job_ptrs *ptrs = &job->ptrs[i];
+
+		if (ptrs->lrc_fence)
+			xe_lrc_free_seqno_fence(ptrs->lrc_fence);
+		if (ptrs->chain_fence)
+			dma_fence_chain_free(ptrs->chain_fence);
+	}
+}
+
 struct xe_sched_job *xe_sched_job_create(struct xe_exec_queue *q,
 					 u64 *batch_addr)
 {
-	struct xe_sched_job *job;
-	struct dma_fence **fences;
 	bool is_migration = xe_sched_job_is_migration(q);
+	struct xe_sched_job *job;
 	int err;
-	int i, j;
+	int i;
 	u32 width;
 
 	/* only a kernel context can submit a vm-less job */
 	XE_WARN_ON(!q->vm && !(q->flags & EXEC_QUEUE_FLAG_KERNEL));
 
-	/* Migration and kernel engines have their own locking */
-	if (!(q->flags & (EXEC_QUEUE_FLAG_KERNEL | EXEC_QUEUE_FLAG_VM))) {
-		lockdep_assert_held(&q->vm->lock);
-		if (!xe_vm_in_lr_mode(q->vm))
-			xe_vm_assert_held(q->vm);
-	}
-
 	job = job_alloc(xe_exec_queue_is_parallel(q) || is_migration);
 	if (!job)
 		return ERR_PTR(-ENOMEM);
@@ -111,63 +118,40 @@ struct xe_sched_job *xe_sched_job_create(struct xe_exec_queue *q,
 	if (err)
 		goto err_free;
 
-	if (!xe_exec_queue_is_parallel(q)) {
-		job->fence = xe_lrc_create_seqno_fence(q->lrc);
-		if (IS_ERR(job->fence)) {
-			err = PTR_ERR(job->fence);
-			goto err_sched_job;
-		}
-		job->lrc_seqno = job->fence->seqno;
-	} else {
-		struct dma_fence_array *cf;
+	for (i = 0; i < q->width; ++i) {
+		struct dma_fence *fence = xe_lrc_alloc_seqno_fence();
+		struct dma_fence_chain *chain;
 
-		fences = kmalloc_array(q->width, sizeof(*fences), GFP_KERNEL);
-		if (!fences) {
-			err = -ENOMEM;
+		if (IS_ERR(fence)) {
+			err = PTR_ERR(fence);
 			goto err_sched_job;
 		}
+		job->ptrs[i].lrc_fence = fence;
 
-		for (j = 0; j < q->width; ++j) {
-			fences[j] = xe_lrc_create_seqno_fence(q->lrc + j);
-			if (IS_ERR(fences[j])) {
-				err = PTR_ERR(fences[j]);
-				goto err_fences;
-			}
-			if (!j)
-				job->lrc_seqno = fences[0]->seqno;
-		}
+		if (i + 1 == q->width)
+			continue;
 
-		cf = dma_fence_array_create(q->width, fences,
-					    q->parallel.composite_fence_ctx,
-					    q->parallel.composite_fence_seqno++,
-					    false);
-		if (!cf) {
-			--q->parallel.composite_fence_seqno;
+		chain = dma_fence_chain_alloc();
+		if (!chain) {
 			err = -ENOMEM;
-			goto err_fences;
+			goto err_sched_job;
 		}
-
-		job->fence = &cf->base;
+		job->ptrs[i].chain_fence = chain;
 	}
 
 	width = q->width;
 	if (is_migration)
 		width = 2;
 
 	for (i = 0; i < width; ++i)
-		job->batch_addr[i] = batch_addr[i];
+		job->ptrs[i].batch_addr = batch_addr[i];
 
 	xe_pm_runtime_get_noresume(job_to_xe(job));
 	trace_xe_sched_job_create(job);
 	return job;
 
-err_fences:
-	for (j = j - 1; j >= 0; --j) {
-		--q->lrc[j].fence_ctx.next_seqno;
-		dma_fence_put(fences[j]);
-	}
-	kfree(fences);
 err_sched_job:
+	xe_sched_job_free_fences(job);
 	drm_sched_job_cleanup(&job->drm);
 err_free:
 	xe_exec_queue_put(q);
@@ -188,34 +172,40 @@ void xe_sched_job_destroy(struct kref *ref)
 		container_of(ref, struct xe_sched_job, refcount);
 	struct xe_device *xe = job_to_xe(job);
 
+	xe_sched_job_free_fences(job);
 	xe_exec_queue_put(job->q);
 	dma_fence_put(job->fence);
 	drm_sched_job_cleanup(&job->drm);
 	job_free(job);
 	xe_pm_runtime_put(xe);
 }
 
-void xe_sched_job_set_error(struct xe_sched_job *job, int error)
+/* Set the error status under the fence to avoid racing with signaling */
+static bool xe_fence_set_error(struct dma_fence *fence, int error)
 {
-	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &job->fence->flags))
-		return;
+	unsigned long irq_flags;
+	bool signaled;
+
+	spin_lock_irqsave(fence->lock, irq_flags);
+	signaled = test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags);
+	if (!signaled)
+		dma_fence_set_error(fence, error);
+	spin_unlock_irqrestore(fence->lock, irq_flags);
 
-	dma_fence_set_error(job->fence, error);
+	return signaled;
+}
 
-	if (dma_fence_is_array(job->fence)) {
-		struct dma_fence_array *array =
-			to_dma_fence_array(job->fence);
-		struct dma_fence **child = array->fences;
-		unsigned int nchild = array->num_fences;
+void xe_sched_job_set_error(struct xe_sched_job *job, int error)
+{
+	if (xe_fence_set_error(job->fence, error))
+		return;
 
-		do {
-			struct dma_fence *current_fence = *child++;
+	if (dma_fence_is_chain(job->fence)) {
+		struct dma_fence *iter;
 
-			if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
-				     &current_fence->flags))
-				continue;
-			dma_fence_set_error(current_fence, error);
-		} while (--nchild);
+		dma_fence_chain_for_each(iter, job->fence)
+			xe_fence_set_error(dma_fence_chain_contained(iter),
+					   error);
 	}
 
 	trace_xe_sched_job_set_error(job);
@@ -230,7 +220,7 @@ bool xe_sched_job_started(struct xe_sched_job *job)
 
 	return !__dma_fence_is_later(xe_sched_job_lrc_seqno(job),
 				     xe_lrc_start_seqno(lrc),
-				     dma_fence_array_first(job->fence)->ops);
+				     dma_fence_chain_contained(job->fence)->ops);
 }
 
 bool xe_sched_job_completed(struct xe_sched_job *job)
@@ -244,13 +234,24 @@ bool xe_sched_job_completed(struct xe_sched_job *job)
 
 	return !__dma_fence_is_later(xe_sched_job_lrc_seqno(job),
 				     xe_lrc_seqno(lrc),
-				     dma_fence_array_first(job->fence)->ops);
+				     dma_fence_chain_contained(job->fence)->ops);
 }
 
 void xe_sched_job_arm(struct xe_sched_job *job)
 {
 	struct xe_exec_queue *q = job->q;
+	struct dma_fence *fence, *prev;
 	struct xe_vm *vm = q->vm;
+	u64 seqno = 0;
+	int i;
+
+	/* Migration and kernel engines have their own locking */
+	if (IS_ENABLED(CONFIG_LOCKDEP) &&
+	    !(q->flags & (EXEC_QUEUE_FLAG_KERNEL | EXEC_QUEUE_FLAG_VM))) {
+		lockdep_assert_held(&q->vm->lock);
+		if (!xe_vm_in_lr_mode(q->vm))
+			xe_vm_assert_held(q->vm);
+	}
 
 	if (vm && !xe_sched_job_is_migration(q) && !xe_vm_in_lr_mode(vm) &&
 	    (vm->batch_invalidate_tlb || vm->tlb_flush_seqno != q->tlb_flush_seqno)) {
@@ -259,6 +260,27 @@ void xe_sched_job_arm(struct xe_sched_job *job)
 		job->ring_ops_flush_tlb = true;
 	}
 
+	/* Arm the pre-allocated fences */
+	for (i = 0; i < q->width; prev = fence, ++i) {
+		struct dma_fence_chain *chain;
+
+		fence = job->ptrs[i].lrc_fence;
+		xe_lrc_init_seqno_fence(&q->lrc[i], fence);
+		job->ptrs[i].lrc_fence = NULL;
+		if (!i) {
+			job->lrc_seqno = fence->seqno;
+			continue;
+		} else {
+			xe_assert(gt_to_xe(q->gt), job->lrc_seqno == fence->seqno);
+		}
+
+		chain = job->ptrs[i - 1].chain_fence;
+		dma_fence_chain_init(chain, prev, fence, seqno++);
+		job->ptrs[i - 1].chain_fence = NULL;
+		fence = &chain->base;
+	}
+
+	job->fence = fence;
 	drm_sched_job_arm(&job->drm);
 }
 
@@ -318,7 +340,8 @@ xe_sched_job_snapshot_capture(struct xe_sched_job *job)
 
 	snapshot->batch_addr_len = q->width;
 	for (i = 0; i < q->width; i++)
-		snapshot->batch_addr[i] = xe_device_uncanonicalize_addr(xe, job->batch_addr[i]);
+		snapshot->batch_addr[i] =
+			xe_device_uncanonicalize_addr(xe, job->ptrs[i].batch_addr);
 
 	return snapshot;
 }

drivers/gpu/drm/xe/xe_sched_job_types.h

@@ -11,6 +11,20 @@
 #include <drm/gpu_scheduler.h>
 
 struct xe_exec_queue;
+struct dma_fence;
+struct dma_fence_chain;
+
+/**
+ * struct xe_job_ptrs - Per hw engine instance data
+ */
+struct xe_job_ptrs {
+	/** @lrc_fence: Pre-allocated uinitialized lrc fence.*/
+	struct dma_fence *lrc_fence;
+	/** @chain_fence: Pre-allocated ninitialized fence chain node. */
+	struct dma_fence_chain *chain_fence;
+	/** @batch_addr: Batch buffer address. */
+	u64 batch_addr;
+};
 
 /**
  * struct xe_sched_job - XE schedule job (batch buffer tracking)
@@ -43,8 +57,8 @@ struct xe_sched_job {
 	u32 migrate_flush_flags;
 	/** @ring_ops_flush_tlb: The ring ops need to flush TLB before payload. */
 	bool ring_ops_flush_tlb;
-	/** @batch_addr: batch buffer address of job */
-	u64 batch_addr[];
+	/** @ptrs: per instance pointers. */
+	struct xe_job_ptrs ptrs[];
 };
 
 struct xe_sched_job_snapshot {