Re: [PATCH 1/8] dma-buf: remove shared fence staging in reservation object

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Ping! Adding a few people directly and more mailing lists.

Can I get an acked-by/rb for this? It's only a cleanup and not much functional change.

Regards,
Christian.

Am 04.10.2018 um 15:12 schrieb Christian König:
No need for that any more. Just replace the list when there isn't enough
room any more for the additional fence.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
  drivers/dma-buf/reservation.c | 178 ++++++++++++++----------------------------
  include/linux/reservation.h   |   4 -
  2 files changed, 58 insertions(+), 124 deletions(-)

diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 6c95f61a32e7..5825fc336a13 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -68,105 +68,23 @@ EXPORT_SYMBOL(reservation_seqcount_string);
   */
  int reservation_object_reserve_shared(struct reservation_object *obj)
  {
-	struct reservation_object_list *fobj, *old;
-	u32 max;
+	struct reservation_object_list *old, *new;
+	unsigned int i, j, k, max;
old = reservation_object_get_list(obj); if (old && old->shared_max) {
-		if (old->shared_count < old->shared_max) {
-			/* perform an in-place update */
-			kfree(obj->staged);
-			obj->staged = NULL;
+		if (old->shared_count < old->shared_max)
  			return 0;
-		} else
+		else
  			max = old->shared_max * 2;
-	} else
-		max = 4;
-
-	/*
-	 * resize obj->staged or allocate if it doesn't exist,
-	 * noop if already correct size
-	 */
-	fobj = krealloc(obj->staged, offsetof(typeof(*fobj), shared[max]),
-			GFP_KERNEL);
-	if (!fobj)
-		return -ENOMEM;
-
-	obj->staged = fobj;
-	fobj->shared_max = max;
-	return 0;
-}
-EXPORT_SYMBOL(reservation_object_reserve_shared);
-
-static void
-reservation_object_add_shared_inplace(struct reservation_object *obj,
-				      struct reservation_object_list *fobj,
-				      struct dma_fence *fence)
-{
-	struct dma_fence *signaled = NULL;
-	u32 i, signaled_idx;
-
-	dma_fence_get(fence);
-
-	preempt_disable();
-	write_seqcount_begin(&obj->seq);
-
-	for (i = 0; i < fobj->shared_count; ++i) {
-		struct dma_fence *old_fence;
-
-		old_fence = rcu_dereference_protected(fobj->shared[i],
-						reservation_object_held(obj));
-
-		if (old_fence->context == fence->context) {
-			/* memory barrier is added by write_seqcount_begin */
-			RCU_INIT_POINTER(fobj->shared[i], fence);
-			write_seqcount_end(&obj->seq);
-			preempt_enable();
-
-			dma_fence_put(old_fence);
-			return;
-		}
-
-		if (!signaled && dma_fence_is_signaled(old_fence)) {
-			signaled = old_fence;
-			signaled_idx = i;
-		}
-	}
-
-	/*
-	 * memory barrier is added by write_seqcount_begin,
-	 * fobj->shared_count is protected by this lock too
-	 */
-	if (signaled) {
-		RCU_INIT_POINTER(fobj->shared[signaled_idx], fence);
  	} else {
-		BUG_ON(fobj->shared_count >= fobj->shared_max);
-		RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence);
-		fobj->shared_count++;
+		max = 4;
  	}
- write_seqcount_end(&obj->seq);
-	preempt_enable();
-
-	dma_fence_put(signaled);
-}
-
-static void
-reservation_object_add_shared_replace(struct reservation_object *obj,
-				      struct reservation_object_list *old,
-				      struct reservation_object_list *fobj,
-				      struct dma_fence *fence)
-{
-	unsigned i, j, k;
-
-	dma_fence_get(fence);
-
-	if (!old) {
-		RCU_INIT_POINTER(fobj->shared[0], fence);
-		fobj->shared_count = 1;
-		goto done;
-	}
+	new = kmalloc(offsetof(typeof(*new), shared[max]), GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
/*
  	 * no need to bump fence refcounts, rcu_read access
@@ -174,46 +92,45 @@ reservation_object_add_shared_replace(struct reservation_object *obj,
  	 * references from the old struct are carried over to
  	 * the new.
  	 */
-	for (i = 0, j = 0, k = fobj->shared_max; i < old->shared_count; ++i) {
-		struct dma_fence *check;
+	for (i = 0, j = 0, k = max; i < (old ? old->shared_count : 0); ++i) {
+		struct dma_fence *fence;
- check = rcu_dereference_protected(old->shared[i],
-						reservation_object_held(obj));
-
-		if (check->context == fence->context ||
-		    dma_fence_is_signaled(check))
-			RCU_INIT_POINTER(fobj->shared[--k], check);
+		fence = rcu_dereference_protected(old->shared[i],
+						  reservation_object_held(obj));
+		if (dma_fence_is_signaled(fence))
+			RCU_INIT_POINTER(new->shared[--k], fence);
  		else
-			RCU_INIT_POINTER(fobj->shared[j++], check);
+			RCU_INIT_POINTER(new->shared[j++], fence);
  	}
-	fobj->shared_count = j;
-	RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence);
-	fobj->shared_count++;
+	new->shared_count = j;
+	new->shared_max = max;
-done:
  	preempt_disable();
  	write_seqcount_begin(&obj->seq);
  	/*
  	 * RCU_INIT_POINTER can be used here,
  	 * seqcount provides the necessary barriers
  	 */
-	RCU_INIT_POINTER(obj->fence, fobj);
+	RCU_INIT_POINTER(obj->fence, new);
  	write_seqcount_end(&obj->seq);
  	preempt_enable();
if (!old)
-		return;
+		return 0;
/* Drop the references to the signaled fences */
-	for (i = k; i < fobj->shared_max; ++i) {
-		struct dma_fence *f;
+	for (i = k; i < new->shared_max; ++i) {
+		struct dma_fence *fence;
- f = rcu_dereference_protected(fobj->shared[i],
-					      reservation_object_held(obj));
-		dma_fence_put(f);
+		fence = rcu_dereference_protected(new->shared[i],
+						  reservation_object_held(obj));
+		dma_fence_put(fence);
  	}
  	kfree_rcu(old, rcu);
+
+	return 0;
  }
+EXPORT_SYMBOL(reservation_object_reserve_shared);
/**
   * reservation_object_add_shared_fence - Add a fence to a shared slot
@@ -226,15 +143,39 @@ reservation_object_add_shared_replace(struct reservation_object *obj,
  void reservation_object_add_shared_fence(struct reservation_object *obj,
  					 struct dma_fence *fence)
  {
-	struct reservation_object_list *old, *fobj = obj->staged;
+	struct reservation_object_list *fobj;
+	unsigned int i;
- old = reservation_object_get_list(obj);
-	obj->staged = NULL;
+	dma_fence_get(fence);
+
+	fobj = reservation_object_get_list(obj);
- if (!fobj)
-		reservation_object_add_shared_inplace(obj, old, fence);
-	else
-		reservation_object_add_shared_replace(obj, old, fobj, fence);
+	preempt_disable();
+	write_seqcount_begin(&obj->seq);
+
+	for (i = 0; i < fobj->shared_count; ++i) {
+		struct dma_fence *old_fence;
+
+		old_fence = rcu_dereference_protected(fobj->shared[i],
+						      reservation_object_held(obj));
+		if (old_fence->context == fence->context ||
+		    dma_fence_is_signaled(old_fence)) {
+			dma_fence_put(old_fence);
+			goto replace;
+		}
+	}
+
+	BUG_ON(fobj->shared_count >= fobj->shared_max);
+	fobj->shared_count++;
+
+replace:
+	/*
+	 * memory barrier is added by write_seqcount_begin,
+	 * fobj->shared_count is protected by this lock too
+	 */
+	RCU_INIT_POINTER(fobj->shared[i], fence);
+	write_seqcount_end(&obj->seq);
+	preempt_enable();
  }
  EXPORT_SYMBOL(reservation_object_add_shared_fence);
@@ -343,9 +284,6 @@ int reservation_object_copy_fences(struct reservation_object *dst,
  	new = dma_fence_get_rcu_safe(&src->fence_excl);
  	rcu_read_unlock();
- kfree(dst->staged);
-	dst->staged = NULL;
-
  	src_list = reservation_object_get_list(dst);
  	old = reservation_object_get_excl(dst);
diff --git a/include/linux/reservation.h b/include/linux/reservation.h
index 02166e815afb..54cf6773a14c 100644
--- a/include/linux/reservation.h
+++ b/include/linux/reservation.h
@@ -68,7 +68,6 @@ struct reservation_object_list {
   * @seq: sequence count for managing RCU read-side synchronization
   * @fence_excl: the exclusive fence, if there is one currently
   * @fence: list of current shared fences
- * @staged: staged copy of shared fences for RCU updates
   */
  struct reservation_object {
  	struct ww_mutex lock;
@@ -76,7 +75,6 @@ struct reservation_object {
struct dma_fence __rcu *fence_excl;
  	struct reservation_object_list __rcu *fence;
-	struct reservation_object_list *staged;
  };
#define reservation_object_held(obj) lockdep_is_held(&(obj)->lock.base)
@@ -95,7 +93,6 @@ reservation_object_init(struct reservation_object *obj)
  	__seqcount_init(&obj->seq, reservation_seqcount_string, &reservation_seqcount_class);
  	RCU_INIT_POINTER(obj->fence, NULL);
  	RCU_INIT_POINTER(obj->fence_excl, NULL);
-	obj->staged = NULL;
  }
/**
@@ -124,7 +121,6 @@ reservation_object_fini(struct reservation_object *obj)
kfree(fobj);
  	}
-	kfree(obj->staged);
ww_mutex_destroy(&obj->lock);
  }




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