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[RFC v2 0/3] dma-buf/sync_file: rework fences on struct sync_file

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  [RFC v2 0/3] dma-buf/sync_file: rework fences on struct sync_file Gustavo Padovan <gustavo@padovan.org> - 2016-06-27 21:30 +0200
    [RFC v2 1/3] dma-buf/fence-array: add fence_is_array() Gustavo Padovan <gustavo@padovan.org> - 2016-06-27 21:40 +0200
    [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown() Gustavo Padovan <gustavo@padovan.org> - 2016-06-27 21:40 +0200
      Re: [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown() Gustavo Padovan <gustavo.padovan@collabora.com> - 2016-06-28 16:20 +0200
        Re: [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown() Gustavo Padovan <gustavo.padovan@collabora.com> - 2016-06-28 17:20 +0200
    [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct file Gustavo Padovan <gustavo@padovan.org> - 2016-06-27 21:40 +0200
      Re: [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct  file Chris Wilson <chris@chris-wilson.co.uk> - 2016-06-28 10:10 +0200
        Re: [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct  file Gustavo Padovan <gustavo.padovan@collabora.com> - 2016-06-28 16:30 +0200
          Re: [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct  file Gustavo Padovan <gustavo.padovan@collabora.com> - 2016-06-28 17:40 +0200
          Re: [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct  file Chris Wilson <chris@chris-wilson.co.uk> - 2016-06-28 18:50 +0200

#1432240 — [RFC v2 0/3] dma-buf/sync_file: rework fences on struct sync_file

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Hi all,

This is an attempt to improve fence support on Sync File. The basic idea
is to have only sync_file->fence and store all fences there, either as
normal fences or fence_arrays. That way we can remove some potential
duplication when using fence_array with sync_file: the duplication of the array
of fences and the duplication of fence_add_callback() for all fences.

Now when creating a new sync_file during the merge process sync_file_set_fence()
will set sync_file->fence based on the number of fences for that sync_file. If
there is more than one fence a fence_array is created. One important advantage
approach is that we only add one fence callback now, no matter how many fences
there are in a sync_file - the individual callbacks are added by fence_array.

Please review! Thanks!

	Gustavo

Changes since v1 (Comments from Chris Wilson and Christian König):
	- Not using fence_ops anymore.
	- fence_is_array() was created to differentiate fence from fence_array
	- fence_array_teardown() is now exported and used under fence_is_array()
	- struct sync_file lost num_fences member

Gustavo Padovan (3):
  dma-buf/fence-array: add fence_is_array()
  dma-buf/fence-array: add fence_array_teardown()
  dma-buf/sync_file: rework fence storage in struct file

 drivers/dma-buf/fence-array.c        |  25 ++++++
 drivers/dma-buf/sync_file.c          | 148 +++++++++++++++++++++++------------
 drivers/staging/android/sync_debug.c |   9 ++-
 include/linux/fence-array.h          |  11 +++
 include/linux/sync_file.h            |  15 ++--
 5 files changed, 147 insertions(+), 61 deletions(-)

-- 
2.5.5

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#1432267 — [RFC v2 1/3] dma-buf/fence-array: add fence_is_array()

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Add helper to check if fence is array.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 include/linux/fence-array.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/fence-array.h b/include/linux/fence-array.h
index 86baaa4..d2e9f40 100644
--- a/include/linux/fence-array.h
+++ b/include/linux/fence-array.h
@@ -52,6 +52,16 @@ struct fence_array {
 extern const struct fence_ops fence_array_ops;
 
 /**
+ * fence_is_array - check if a fence is from the array subsclass
+ *
+ * Return true if it is a fence_array and false otherwise.
+ */
+static inline bool fence_is_array(struct fence *fence)
+{
+	return (fence->ops == &fence_array_ops) ? true : false;
+}
+
+/**
  * to_fence_array - cast a fence to a fence_array
  * @fence: fence to cast to a fence_array
  *
-- 
2.5.5

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#1432271 — [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown()

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

As the array of fence callbacks held by an active struct fence_array
each has a reference to the struct fence_array, when the owner of the
fence_array is freed it must dispose of the callback references before
it can free the fence_array. This can not happen simply during
fence_release() because of the extra references and so we need a new
function to run before the final fence_put().

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 drivers/dma-buf/fence-array.c | 25 +++++++++++++++++++++++++
 include/linux/fence-array.h   |  1 +
 2 files changed, 26 insertions(+)

diff --git a/drivers/dma-buf/fence-array.c b/drivers/dma-buf/fence-array.c
index a8731c8..8891357 100644
--- a/drivers/dma-buf/fence-array.c
+++ b/drivers/dma-buf/fence-array.c
@@ -142,3 +142,28 @@ struct fence_array *fence_array_create(int num_fences, struct fence **fences,
 	return array;
 }
 EXPORT_SYMBOL(fence_array_create);
+
+/**
+ * fence_array_teardown - Teardown and clean up a fence array
+ * @array:	[in]	the fence array to teardown
+ *
+ * This function removes callbacks and extra references to the base fence on
+ * the fence_array for each unsignalled fence in the array. It should be called
+ * before calling fence_put() to remove the last reference on a fence_array,
+ * otherwise the fence won't be released due to extra references holded by the
+ * the fences that still have signalling enabled.
+ */
+void fence_array_teardown(struct fence_array *array)
+{
+	struct fence_array_cb *cb = (void *)(&array[1]);
+	int i;
+
+	for (i = 0; i < array->num_fences; i++) {
+		if (fence_is_signaled(array->fences[i]))
+		    continue;
+
+		fence_remove_callback(array->fences[i], &cb[i].cb);
+		fence_put(&array->base);
+	}
+}
+EXPORT_SYMBOL(fence_array_teardown);
diff --git a/include/linux/fence-array.h b/include/linux/fence-array.h
index d2e9f40..9f1b923 100644
--- a/include/linux/fence-array.h
+++ b/include/linux/fence-array.h
@@ -79,5 +79,6 @@ static inline struct fence_array *to_fence_array(struct fence *fence)
 struct fence_array *fence_array_create(int num_fences, struct fence **fences,
 				       u64 context, unsigned seqno,
 				       bool signal_on_any);
+void fence_array_teardown(struct fence_array *array);
 
 #endif /* __LINUX_FENCE_ARRAY_H */
-- 
2.5.5

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#1433020 — Re: [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown()

2016-06-28 Christian König <christian.koenig@amd.com>:

> Am 27.06.2016 um 21:29 schrieb Gustavo Padovan:
> > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > 
> > As the array of fence callbacks held by an active struct fence_array
> > each has a reference to the struct fence_array, when the owner of the
> > fence_array is freed it must dispose of the callback references before
> > it can free the fence_array. This can not happen simply during
> > fence_release() because of the extra references and so we need a new
> > function to run before the final fence_put().
> 
> As I said previously as well, this is completely superfluous.
> 
> The fence array keeps a reference to itself as long as not all callbacks are
> signaled.
> 
> So you only need to unregister your callback from the array itself and drop
> your reference when you don't need it any more in the sync file.

Exactly, this should be called from sync_file_free() because of the
following use case:

	1. You create 2 sync_file with 1 fence each
	2. Merge both fences, which creates a fence array
	3. Close the sync_file fd without waiting for the fences to
	signal

At this point you leak the fence-array because the final fence_put() 
does not release it because of the extra references from the non
signalled fences so we need to clean up this somehow.

	Gustavo

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#1433054 — Re: [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown()

2016-06-28 Christian König <christian.koenig@amd.com>:

> Am 28.06.2016 um 16:17 schrieb Gustavo Padovan:
> > 2016-06-28 Christian König <christian.koenig@amd.com>:
> > 
> > > Am 27.06.2016 um 21:29 schrieb Gustavo Padovan:
> > > > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > > 
> > > > As the array of fence callbacks held by an active struct fence_array
> > > > each has a reference to the struct fence_array, when the owner of the
> > > > fence_array is freed it must dispose of the callback references before
> > > > it can free the fence_array. This can not happen simply during
> > > > fence_release() because of the extra references and so we need a new
> > > > function to run before the final fence_put().
> > > As I said previously as well, this is completely superfluous.
> > > 
> > > The fence array keeps a reference to itself as long as not all callbacks are
> > > signaled.
> > > 
> > > So you only need to unregister your callback from the array itself and drop
> > > your reference when you don't need it any more in the sync file.
> > Exactly, this should be called from sync_file_free() because of the
> > following use case:
> > 
> > 	1. You create 2 sync_file with 1 fence each
> > 	2. Merge both fences, which creates a fence array
> > 	3. Close the sync_file fd without waiting for the fences to
> > 	signal
> > 
> > At this point you leak the fence-array because the final fence_put()
> > does not release it because of the extra references from the non
> > signalled fences so we need to clean up this somehow.
> 
> No, there won't be any leak and you don't need to cleanup anything.
> 
> The fences contained in the fence array are already enabled for signaling.
> So they will eventually signal sooner or later and drop the reference to the
> fence array freeing it when the last one finished.
> 
> This was done to avoid the need to call fence_remove_callback() all the time
> on the fences in the array because of the warning on the function.

Right. I understand it now.

	Gustavo

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#1432278 — [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct file

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Create sync_file->fence to abstract the type of fence we are using for
each sync_file. If only one fence is present we use a normal struct fence
but if there is more fences to be added to the sync_file a fence_array
is created.

This change cleans up sync_file a bit. We don't need to have sync_file_cb
array anymore. Instead, as we always have  one fence, only one fence
callback is registered per sync_file.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 drivers/dma-buf/sync_file.c          | 148 +++++++++++++++++++++++------------
 drivers/staging/android/sync_debug.c |   9 ++-
 include/linux/sync_file.h            |  15 ++--
 3 files changed, 111 insertions(+), 61 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 9aaa608..ca19d3a 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -28,11 +28,11 @@
 
 static const struct file_operations sync_file_fops;
 
-static struct sync_file *sync_file_alloc(int size)
+static struct sync_file *sync_file_alloc(void)
 {
 	struct sync_file *sync_file;
 
-	sync_file = kzalloc(size, GFP_KERNEL);
+	sync_file = kzalloc(sizeof(*sync_file), GFP_KERNEL);
 	if (!sync_file)
 		return NULL;
 
@@ -45,6 +45,8 @@ static struct sync_file *sync_file_alloc(int size)
 
 	init_waitqueue_head(&sync_file->wq);
 
+	INIT_LIST_HEAD(&sync_file->cb.node);
+
 	return sync_file;
 
 err:
@@ -54,11 +56,9 @@ err:
 
 static void fence_check_cb_func(struct fence *f, struct fence_cb *cb)
 {
-	struct sync_file_cb *check;
 	struct sync_file *sync_file;
 
-	check = container_of(cb, struct sync_file_cb, cb);
-	sync_file = check->sync_file;
+	sync_file = container_of(cb, struct sync_file, cb);
 
 	if (atomic_dec_and_test(&sync_file->status))
 		wake_up_all(&sync_file->wq);
@@ -76,21 +76,19 @@ struct sync_file *sync_file_create(struct fence *fence)
 {
 	struct sync_file *sync_file;
 
-	sync_file = sync_file_alloc(offsetof(struct sync_file, cbs[1]));
+	sync_file = sync_file_alloc();
 	if (!sync_file)
 		return NULL;
 
-	sync_file->num_fences = 1;
+	sync_file->fence = fence;
+
 	atomic_set(&sync_file->status, 1);
 	snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d",
 		 fence->ops->get_driver_name(fence),
 		 fence->ops->get_timeline_name(fence), fence->context,
 		 fence->seqno);
 
-	sync_file->cbs[0].fence = fence;
-	sync_file->cbs[0].sync_file = sync_file;
-	if (fence_add_callback(fence, &sync_file->cbs[0].cb,
-			       fence_check_cb_func))
+	if (fence_add_callback(fence, &sync_file->cb, fence_check_cb_func))
 		atomic_dec(&sync_file->status);
 
 	return sync_file;
@@ -121,14 +119,42 @@ err:
 	return NULL;
 }
 
-static void sync_file_add_pt(struct sync_file *sync_file, int *i,
-			     struct fence *fence)
+static int sync_file_set_fence(struct sync_file *sync_file,
+			       struct fence **fences, int num_fences)
 {
-	sync_file->cbs[*i].fence = fence;
-	sync_file->cbs[*i].sync_file = sync_file;
+	struct fence_array *array;
+
+	if (num_fences == 1) {
+		sync_file->fence = fences[0];
+	} else {
+		array = fence_array_create(num_fences, fences,
+					   fence_context_alloc(1), 1, false);
+		if (!array)
+			return -ENOMEM;
+
+		sync_file->fence = (struct fence *)array;
+	}
+
+	return 0;
+}
 
-	if (!fence_add_callback(fence, &sync_file->cbs[*i].cb,
-				fence_check_cb_func)) {
+static struct fence **get_fences(struct sync_file *sync_file, int *num_fences)
+{
+	if (fence_is_array(sync_file->fence)) {
+		struct fence_array *array = to_fence_array(sync_file->fence);
+		*num_fences = array->num_fences;
+		return array->fences;
+	} else {
+		*num_fences = 1;
+		return &sync_file->fence;
+	}
+}
+
+static void add_fence(struct fence **fences, int *i, struct fence *fence)
+{
+	fences[*i] = fence;
+
+	if (!fence_is_signaled(fence)) {
 		fence_get(fence);
 		(*i)++;
 	}
@@ -147,16 +173,23 @@ static void sync_file_add_pt(struct sync_file *sync_file, int *i,
 static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 					 struct sync_file *b)
 {
-	int num_fences = a->num_fences + b->num_fences;
 	struct sync_file *sync_file;
-	int i, i_a, i_b;
-	unsigned long size = offsetof(struct sync_file, cbs[num_fences]);
+	struct fence **fences, **a_fences, **b_fences;
+	int i, i_a, i_b, num_fences, a_num_fences, b_num_fences;
 
-	sync_file = sync_file_alloc(size);
+	sync_file = sync_file_alloc();
 	if (!sync_file)
 		return NULL;
 
-	atomic_set(&sync_file->status, num_fences);
+	a_fences = get_fences(a, &a_num_fences);
+	b_fences = get_fences(b, &b_num_fences);
+	num_fences = a_num_fences + b_num_fences;
+
+	fences = kcalloc(num_fences, sizeof(**fences), GFP_KERNEL);
+	if (!fences)
+		goto err;
+
+	atomic_set(&sync_file->status, 1);
 
 	/*
 	 * Assume sync_file a and b are both ordered and have no
@@ -165,55 +198,69 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 	 * If a sync_file can only be created with sync_file_merge
 	 * and sync_file_create, this is a reasonable assumption.
 	 */
-	for (i = i_a = i_b = 0; i_a < a->num_fences && i_b < b->num_fences; ) {
-		struct fence *pt_a = a->cbs[i_a].fence;
-		struct fence *pt_b = b->cbs[i_b].fence;
+	for (i = i_a = i_b = 0; i_a < a_num_fences && i_b < b_num_fences; ) {
+		struct fence *pt_a = a_fences[i_a];
+		struct fence *pt_b = b_fences[i_b];
 
 		if (pt_a->context < pt_b->context) {
-			sync_file_add_pt(sync_file, &i, pt_a);
+			add_fence(fences, &i, pt_a);
 
 			i_a++;
 		} else if (pt_a->context > pt_b->context) {
-			sync_file_add_pt(sync_file, &i, pt_b);
+			add_fence(fences, &i, pt_b);
 
 			i_b++;
 		} else {
 			if (pt_a->seqno - pt_b->seqno <= INT_MAX)
-				sync_file_add_pt(sync_file, &i, pt_a);
+				add_fence(fences, &i, pt_a);
 			else
-				sync_file_add_pt(sync_file, &i, pt_b);
+				add_fence(fences, &i, pt_b);
 
 			i_a++;
 			i_b++;
 		}
 	}
 
-	for (; i_a < a->num_fences; i_a++)
-		sync_file_add_pt(sync_file, &i, a->cbs[i_a].fence);
+	for (; i_a < a_num_fences; i_a++)
+		add_fence(fences, &i, a_fences[i_a]);
+
+	for (; i_b < b_num_fences; i_b++)
+		add_fence(fences, &i, b_fences[i_b]);
+
+	if (num_fences > i) {
+		fences = krealloc(fences, i * sizeof(**fences),
+				  GFP_KERNEL);
+		if (!fences)
+			goto err;
+	}
 
-	for (; i_b < b->num_fences; i_b++)
-		sync_file_add_pt(sync_file, &i, b->cbs[i_b].fence);
+	if (sync_file_set_fence(sync_file, fences, i) < 0) {
+		kfree(fences);
+		goto err;
+	}
 
-	if (num_fences > i)
-		atomic_sub(num_fences - i, &sync_file->status);
-	sync_file->num_fences = i;
+	if (fence_add_callback(sync_file->fence, &sync_file->cb,
+			       fence_check_cb_func))
+		atomic_dec(&sync_file->status);
 
 	strlcpy(sync_file->name, name, sizeof(sync_file->name));
 	return sync_file;
+
+err:
+	fput(sync_file->file);
+	return NULL;
+
 }
 
 static void sync_file_free(struct kref *kref)
 {
 	struct sync_file *sync_file = container_of(kref, struct sync_file,
 						     kref);
-	int i;
-
-	for (i = 0; i < sync_file->num_fences; ++i) {
-		fence_remove_callback(sync_file->cbs[i].fence,
-				      &sync_file->cbs[i].cb);
-		fence_put(sync_file->cbs[i].fence);
-	}
 
+	fence_remove_callback(sync_file->fence, &sync_file->cb);
+	if (fence_is_array(sync_file->fence))
+		fence_array_teardown(to_fence_array(sync_file->fence));
+	fence_put(sync_file->fence);
 	kfree(sync_file);
 }
 
@@ -315,8 +362,9 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 {
 	struct sync_file_info info;
 	struct sync_fence_info *fence_info = NULL;
+	struct fence **fences;
 	__u32 size;
-	int ret, i;
+	int num_fences, ret, i;
 
 	if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
 		return -EFAULT;
@@ -324,6 +372,8 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (info.flags || info.pad)
 		return -EINVAL;
 
+	fences = get_fences(sync_file, &num_fences);
+
 	/*
 	 * Passing num_fences = 0 means that userspace doesn't want to
 	 * retrieve any sync_fence_info. If num_fences = 0 we skip filling
@@ -333,16 +383,16 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (!info.num_fences)
 		goto no_fences;
 
-	if (info.num_fences < sync_file->num_fences)
+	if (info.num_fences < num_fences)
 		return -EINVAL;
 
-	size = sync_file->num_fences * sizeof(*fence_info);
+	size = num_fences * sizeof(*fence_info);
 	fence_info = kzalloc(size, GFP_KERNEL);
 	if (!fence_info)
 		return -ENOMEM;
 
-	for (i = 0; i < sync_file->num_fences; ++i)
-		sync_fill_fence_info(sync_file->cbs[i].fence, &fence_info[i]);
+	for (i = 0; i < num_fences; i++)
+		sync_fill_fence_info(fences[i], &fence_info[i]);
 
 	if (copy_to_user(u64_to_user_ptr(info.sync_fence_info), fence_info,
 			 size)) {
@@ -356,7 +406,7 @@ no_fences:
 	if (info.status >= 0)
 		info.status = !info.status;
 
-	info.num_fences = sync_file->num_fences;
+	info.num_fences = num_fences;
 
 	if (copy_to_user((void __user *)arg, &info, sizeof(info)))
 		ret = -EFAULT;
diff --git a/drivers/staging/android/sync_debug.c b/drivers/staging/android/sync_debug.c
index 5f57499..259a20d 100644
--- a/drivers/staging/android/sync_debug.c
+++ b/drivers/staging/android/sync_debug.c
@@ -161,8 +161,13 @@ static void sync_print_sync_file(struct seq_file *s,
 	seq_printf(s, "[%p] %s: %s\n", sync_file, sync_file->name,
 		   sync_status_str(atomic_read(&sync_file->status)));
 
-	for (i = 0; i < sync_file->num_fences; ++i)
-		sync_print_fence(s, sync_file->cbs[i].fence, true);
+	if (fence_is_array(sync_file->fence)) {
+		struct fence_array *array = to_fence_array(sync_file->fence);
+		for (i = 0; i < array->num_fences; ++i)
+			sync_print_fence(s, array->fences[i], true);
+	} else {
+		sync_print_fence(s, sync_file->fence, true);
+	}
 }
 
 static int sync_debugfs_show(struct seq_file *s, void *unused)
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index c6ffe8b..7313208 100644
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -19,12 +19,7 @@
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/fence.h>
-
-struct sync_file_cb {
-	struct fence_cb cb;
-	struct fence *fence;
-	struct sync_file *sync_file;
-};
+#include <linux/fence-array.h>
 
 /**
  * struct sync_file - sync file to export to the userspace
@@ -32,10 +27,10 @@ struct sync_file_cb {
  * @kref:		reference count on fence.
  * @name:		name of sync_file.  Useful for debugging
  * @sync_file_list:	membership in global file list
- * @num_fences:		number of sync_pts in the fence
  * @wq:			wait queue for fence signaling
  * @status:		0: signaled, >0:active, <0: error
- * @cbs:		sync_pts callback information
+ * @fence:		fence with the fences in the sync_file
+ * @cb:			fence callback information
  */
 struct sync_file {
 	struct file		*file;
@@ -44,12 +39,12 @@ struct sync_file {
 #ifdef CONFIG_DEBUG_FS
 	struct list_head	sync_file_list;
 #endif
-	int num_fences;
 
 	wait_queue_head_t	wq;
 	atomic_t		status;
 
-	struct sync_file_cb	cbs[];
+	struct fence		*fence;
+	struct fence_cb cb;
 };
 
 struct sync_file *sync_file_create(struct fence *fence);
-- 
2.5.5

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#1432609 — Re: [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct file

On Mon, Jun 27, 2016 at 04:29:22PM -0300, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> 
> Create sync_file->fence to abstract the type of fence we are using for
> each sync_file. If only one fence is present we use a normal struct fence
> but if there is more fences to be added to the sync_file a fence_array
> is created.
> 
> This change cleans up sync_file a bit. We don't need to have sync_file_cb
> array anymore. Instead, as we always have  one fence, only one fence
> callback is registered per sync_file.
> 
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> ---
> @@ -76,21 +76,19 @@ struct sync_file *sync_file_create(struct fence *fence)
>  {
>  	struct sync_file *sync_file;
>  
> -	sync_file = sync_file_alloc(offsetof(struct sync_file, cbs[1]));
> +	sync_file = sync_file_alloc();
>  	if (!sync_file)
>  		return NULL;
>  
> -	sync_file->num_fences = 1;
> +	sync_file->fence = fence;
> +
>  	atomic_set(&sync_file->status, 1);

sync_file->status => fence_is_signaled(sync_file->fence);

Both should just be an atomic read, except fence_is_signaled() will then
do a secondary poll.

>  	snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d",
>  		 fence->ops->get_driver_name(fence),
>  		 fence->ops->get_timeline_name(fence), fence->context,
>  		 fence->seqno);
>  
> -	sync_file->cbs[0].fence = fence;
> -	sync_file->cbs[0].sync_file = sync_file;
> -	if (fence_add_callback(fence, &sync_file->cbs[0].cb,
> -			       fence_check_cb_func))
> +	if (fence_add_callback(fence, &sync_file->cb, fence_check_cb_func))
>  		atomic_dec(&sync_file->status);
>  
>  	return sync_file;
> @@ -121,14 +119,42 @@ err:
>  	return NULL;
>  }
>  
> -static void sync_file_add_pt(struct sync_file *sync_file, int *i,
> -			     struct fence *fence)
> +static int sync_file_set_fence(struct sync_file *sync_file,
> +			       struct fence **fences, int num_fences)
>  {
> -	sync_file->cbs[*i].fence = fence;
> -	sync_file->cbs[*i].sync_file = sync_file;
> +	struct fence_array *array;
> +
> +	if (num_fences == 1) {
> +		sync_file->fence = fences[0];

This steals the references.

> +	} else {
> +		array = fence_array_create(num_fences, fences,
> +					   fence_context_alloc(1), 1, false);

This creates a reference.

When we call fence_put(sync_fence->fence) we release a reference we
never owned if num_fences == 1.

> +	struct fence **fences, **a_fences, **b_fences;
> +	int i, i_a, i_b, num_fences, a_num_fences, b_num_fences;
>  
> +	a_fences = get_fences(a, &a_num_fences);
> +	b_fences = get_fences(b, &b_num_fences);
> +	num_fences = a_num_fences + b_num_fences;
> +
> +	fences = kcalloc(num_fences, sizeof(**fences), GFP_KERNEL);

Just sizeof(*fences) (you want to allocate an array of pointers, not an
array of fence structs).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

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#1433028 — Re: [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct file

2016-06-28 Chris Wilson <chris@chris-wilson.co.uk>:

> On Mon, Jun 27, 2016 at 04:29:22PM -0300, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > 
> > Create sync_file->fence to abstract the type of fence we are using for
> > each sync_file. If only one fence is present we use a normal struct fence
> > but if there is more fences to be added to the sync_file a fence_array
> > is created.
> > 
> > This change cleans up sync_file a bit. We don't need to have sync_file_cb
> > array anymore. Instead, as we always have  one fence, only one fence
> > callback is registered per sync_file.
> > 
> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Christian König <christian.koenig@amd.com>
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > ---
> > @@ -76,21 +76,19 @@ struct sync_file *sync_file_create(struct fence *fence)
> >  {
> >  	struct sync_file *sync_file;
> >  
> > -	sync_file = sync_file_alloc(offsetof(struct sync_file, cbs[1]));
> > +	sync_file = sync_file_alloc();
> >  	if (!sync_file)
> >  		return NULL;
> >  
> > -	sync_file->num_fences = 1;
> > +	sync_file->fence = fence;
> > +
> >  	atomic_set(&sync_file->status, 1);
> 
> sync_file->status => fence_is_signaled(sync_file->fence);
> 
> Both should just be an atomic read, except fence_is_signaled() will then
> do a secondary poll.

Not sure I follow. I set it to 1 here, but below when we call
fence_add_callback() and the fence is already signalled atomic_dec sets
sync_file->status to 0.

> 
> >  	snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d",
> >  		 fence->ops->get_driver_name(fence),
> >  		 fence->ops->get_timeline_name(fence), fence->context,
> >  		 fence->seqno);
> >  
> > -	sync_file->cbs[0].fence = fence;
> > -	sync_file->cbs[0].sync_file = sync_file;
> > -	if (fence_add_callback(fence, &sync_file->cbs[0].cb,
> > -			       fence_check_cb_func))
> > +	if (fence_add_callback(fence, &sync_file->cb, fence_check_cb_func))
> >  		atomic_dec(&sync_file->status);
> >  
> >  	return sync_file;
> > @@ -121,14 +119,42 @@ err:
> >  	return NULL;
> >  }
> >  
> > -static void sync_file_add_pt(struct sync_file *sync_file, int *i,
> > -			     struct fence *fence)
> > +static int sync_file_set_fence(struct sync_file *sync_file,
> > +			       struct fence **fences, int num_fences)
> >  {
> > -	sync_file->cbs[*i].fence = fence;
> > -	sync_file->cbs[*i].sync_file = sync_file;
> > +	struct fence_array *array;
> > +
> > +	if (num_fences == 1) {
> > +		sync_file->fence = fences[0];
> 
> This steals the references.
> 
> > +	} else {
> > +		array = fence_array_create(num_fences, fences,
> > +					   fence_context_alloc(1), 1, false);
> 
> This creates a reference.
> 
> When we call fence_put(sync_fence->fence) we release a reference we
> never owned if num_fences == 1.

No, sync_file_merge() gets a new reference for each fence it is going to
add to the new fence. So for num_fences == 1 when sync_file->fence is
set we already hold a reference to it, so no matter if it is a fence or
a array we own a reference.

> 
> > +	struct fence **fences, **a_fences, **b_fences;
> > +	int i, i_a, i_b, num_fences, a_num_fences, b_num_fences;
> >  
> > +	a_fences = get_fences(a, &a_num_fences);
> > +	b_fences = get_fences(b, &b_num_fences);
> > +	num_fences = a_num_fences + b_num_fences;
> > +
> > +	fences = kcalloc(num_fences, sizeof(**fences), GFP_KERNEL);
> 
> Just sizeof(*fences) (you want to allocate an array of pointers, not an
> array of fence structs).

Okay.

	Gustavo

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#1433070 — Re: [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct file

2016-06-28 Chris Wilson <chris@chris-wilson.co.uk>:

> On Tue, Jun 28, 2016 at 11:25:00AM -0300, Gustavo Padovan wrote:
> > 2016-06-28 Chris Wilson <chris@chris-wilson.co.uk>:
> > 
> > > On Mon, Jun 27, 2016 at 04:29:22PM -0300, Gustavo Padovan wrote:
> > > > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > > 
> > > > Create sync_file->fence to abstract the type of fence we are using for
> > > > each sync_file. If only one fence is present we use a normal struct fence
> > > > but if there is more fences to be added to the sync_file a fence_array
> > > > is created.
> > > > 
> > > > This change cleans up sync_file a bit. We don't need to have sync_file_cb
> > > > array anymore. Instead, as we always have  one fence, only one fence
> > > > callback is registered per sync_file.
> > > > 
> > > > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > > Cc: Christian König <christian.koenig@amd.com>
> > > > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > > ---
> > > > @@ -76,21 +76,19 @@ struct sync_file *sync_file_create(struct fence *fence)
> > > >  {
> > > >  	struct sync_file *sync_file;
> > > >  
> > > > -	sync_file = sync_file_alloc(offsetof(struct sync_file, cbs[1]));
> > > > +	sync_file = sync_file_alloc();
> > > >  	if (!sync_file)
> > > >  		return NULL;
> > > >  
> > > > -	sync_file->num_fences = 1;
> > > > +	sync_file->fence = fence;
> > > > +
> > > >  	atomic_set(&sync_file->status, 1);
> > > 
> > > sync_file->status => fence_is_signaled(sync_file->fence);
> > > 
> > > Both should just be an atomic read, except fence_is_signaled() will then
> > > do a secondary poll.
> > 
> > Not sure I follow. I set it to 1 here, but below when we call
> > fence_add_callback() and the fence is already signalled atomic_dec sets
> > sync_file->status to 0.
> 
> I'm just saying that usage sync_file->status is equivalent to
> fence_is_signaled(), i.e. we reduce the amount of bookkeeping local to
> sync_file.

Indeed, that makes sense, I'll remove status from sync_file.

> 
> > > >  	snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d",
> > > >  		 fence->ops->get_driver_name(fence),
> > > >  		 fence->ops->get_timeline_name(fence), fence->context,
> > > >  		 fence->seqno);
> > > >  
> > > > -	sync_file->cbs[0].fence = fence;
> > > > -	sync_file->cbs[0].sync_file = sync_file;
> > > > -	if (fence_add_callback(fence, &sync_file->cbs[0].cb,
> > > > -			       fence_check_cb_func))
> > > > +	if (fence_add_callback(fence, &sync_file->cb, fence_check_cb_func))
> > > >  		atomic_dec(&sync_file->status);
> > > >  
> > > >  	return sync_file;
> > > > @@ -121,14 +119,42 @@ err:
> > > >  	return NULL;
> > > >  }
> > > >  
> > > > -static void sync_file_add_pt(struct sync_file *sync_file, int *i,
> > > > -			     struct fence *fence)
> > > > +static int sync_file_set_fence(struct sync_file *sync_file,
> > > > +			       struct fence **fences, int num_fences)
> > > >  {
> > > > -	sync_file->cbs[*i].fence = fence;
> > > > -	sync_file->cbs[*i].sync_file = sync_file;
> > > > +	struct fence_array *array;
> > > > +
> > > > +	if (num_fences == 1) {
> > > > +		sync_file->fence = fences[0];
> > > 
> > > This steals the references.
> > > 
> > > > +	} else {
> > > > +		array = fence_array_create(num_fences, fences,
> > > > +					   fence_context_alloc(1), 1, false);
> > > 
> > > This creates a reference.
> > > 
> > > When we call fence_put(sync_fence->fence) we release a reference we
> > > never owned if num_fences == 1.
> > 
> > No, sync_file_merge() gets a new reference for each fence it is going to
> > add to the new fence. So for num_fences == 1 when sync_file->fence is
> > set we already hold a reference to it, so no matter if it is a fence or
> > a array we own a reference.
> 
> Ugh. Root cause appears to be that fence_array_create() does not behave
> how I would expect, in that it borrows references to the fences and
> not own a reference to the fences in its array. I beg for a comment as
> this function is very counter-intuitive for me.

There is this in fence_array_create():

 * The caller should allocte the fences array with num_fences size              
 * and fill it with the fences it wants to add to the object. Ownership of this 
 * array is take and fence_put() is used on each fence on release.     

	Gustavo

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#1433117 — Re: [RFC v2 3/3] dma-buf/sync_file: rework fence storage in struct file

On Tue, Jun 28, 2016 at 11:25:00AM -0300, Gustavo Padovan wrote:
> 2016-06-28 Chris Wilson <chris@chris-wilson.co.uk>:
> 
> > On Mon, Jun 27, 2016 at 04:29:22PM -0300, Gustavo Padovan wrote:
> > > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > 
> > > Create sync_file->fence to abstract the type of fence we are using for
> > > each sync_file. If only one fence is present we use a normal struct fence
> > > but if there is more fences to be added to the sync_file a fence_array
> > > is created.
> > > 
> > > This change cleans up sync_file a bit. We don't need to have sync_file_cb
> > > array anymore. Instead, as we always have  one fence, only one fence
> > > callback is registered per sync_file.
> > > 
> > > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > Cc: Christian König <christian.koenig@amd.com>
> > > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > ---
> > > @@ -76,21 +76,19 @@ struct sync_file *sync_file_create(struct fence *fence)
> > >  {
> > >  	struct sync_file *sync_file;
> > >  
> > > -	sync_file = sync_file_alloc(offsetof(struct sync_file, cbs[1]));
> > > +	sync_file = sync_file_alloc();
> > >  	if (!sync_file)
> > >  		return NULL;
> > >  
> > > -	sync_file->num_fences = 1;
> > > +	sync_file->fence = fence;
> > > +
> > >  	atomic_set(&sync_file->status, 1);
> > 
> > sync_file->status => fence_is_signaled(sync_file->fence);
> > 
> > Both should just be an atomic read, except fence_is_signaled() will then
> > do a secondary poll.
> 
> Not sure I follow. I set it to 1 here, but below when we call
> fence_add_callback() and the fence is already signalled atomic_dec sets
> sync_file->status to 0.

I'm just saying that usage sync_file->status is equivalent to
fence_is_signaled(), i.e. we reduce the amount of bookkeeping local to
sync_file.

> > >  	snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d",
> > >  		 fence->ops->get_driver_name(fence),
> > >  		 fence->ops->get_timeline_name(fence), fence->context,
> > >  		 fence->seqno);
> > >  
> > > -	sync_file->cbs[0].fence = fence;
> > > -	sync_file->cbs[0].sync_file = sync_file;
> > > -	if (fence_add_callback(fence, &sync_file->cbs[0].cb,
> > > -			       fence_check_cb_func))
> > > +	if (fence_add_callback(fence, &sync_file->cb, fence_check_cb_func))
> > >  		atomic_dec(&sync_file->status);
> > >  
> > >  	return sync_file;
> > > @@ -121,14 +119,42 @@ err:
> > >  	return NULL;
> > >  }
> > >  
> > > -static void sync_file_add_pt(struct sync_file *sync_file, int *i,
> > > -			     struct fence *fence)
> > > +static int sync_file_set_fence(struct sync_file *sync_file,
> > > +			       struct fence **fences, int num_fences)
> > >  {
> > > -	sync_file->cbs[*i].fence = fence;
> > > -	sync_file->cbs[*i].sync_file = sync_file;
> > > +	struct fence_array *array;
> > > +
> > > +	if (num_fences == 1) {
> > > +		sync_file->fence = fences[0];
> > 
> > This steals the references.
> > 
> > > +	} else {
> > > +		array = fence_array_create(num_fences, fences,
> > > +					   fence_context_alloc(1), 1, false);
> > 
> > This creates a reference.
> > 
> > When we call fence_put(sync_fence->fence) we release a reference we
> > never owned if num_fences == 1.
> 
> No, sync_file_merge() gets a new reference for each fence it is going to
> add to the new fence. So for num_fences == 1 when sync_file->fence is
> set we already hold a reference to it, so no matter if it is a fence or
> a array we own a reference.

Ugh. Root cause appears to be that fence_array_create() does not behave
how I would expect, in that it borrows references to the fences and
not own a reference to the fences in its array. I beg for a comment as
this function is very counter-intuitive for me.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

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