[PATCH 1/3] dma-buf/sync_file: cleanup fence merging a bit

[PATCH 1/3] dma-buf/sync_file: cleanup fence merging a bit

[Christian König]

krealloc_array() ignores attempts to reduce the array size, so the attempt
to save memory is completely pointless here.

Also move testing for the no fence case into sync_file_set_fence(), this
way we don't even touch the fence array when we don't have any fences.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/sync_file.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 514d213261df..0fe564539166 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -157,9 +157,15 @@ static int sync_file_set_fence(struct sync_file *sync_file,
 	 * we already own a new reference to the fence. For num_fence > 1
 	 * we own the reference of the dma_fence_array creation.
 	 */
-	if (num_fences == 1) {
+
+	if (num_fences == 0) {
+		sync_file->fence = dma_fence_get_stub();
+		kfree(fences);
+
+	} else if (num_fences == 1) {
 		sync_file->fence = fences[0];
 		kfree(fences);
+
 	} else {
 		array = dma_fence_array_create(num_fences, fences,
 					       dma_fence_context_alloc(1),
@@ -261,19 +267,6 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 		}
 	}
 
-	if (index == 0)
-		fences[index++] = dma_fence_get_stub();
-
-	if (num_fences > index) {
-		struct dma_fence **tmp;
-
-		/* Keep going even when reducing the size failed */
-		tmp = krealloc_array(fences, index, sizeof(*fences),
-				     GFP_KERNEL);
-		if (tmp)
-			fences = tmp;
-	}
-
 	if (sync_file_set_fence(sync_file, fences, index) < 0)
 		goto err_put_fences;
 
-- 
2.25.1

[PATCH 2/3] dma-buf: cleanup dma_fence_unwrap implementation and selftest

[Christian König]

Move the code from the inline functions into exported functions.

While at it also cleanup the the selftests, fix the error handling,
remove unused functions and stop leaking memory in failed tests.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/Makefile              |  2 +-
 drivers/dma-buf/dma-fence-unwrap.c    | 59 +++++++++++++++++++++++++++
 drivers/dma-buf/st-dma-fence-unwrap.c | 40 ++++++++----------
 include/linux/dma-fence-unwrap.h      | 52 ++---------------------
 4 files changed, 80 insertions(+), 73 deletions(-)
 create mode 100644 drivers/dma-buf/dma-fence-unwrap.c

diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index 4c9eb53ba3f8..70ec901edf2c 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
-	 dma-resv.o
+	 dma-fence-unwrap.o dma-resv.o
 obj-$(CONFIG_DMABUF_HEAPS)	+= dma-heap.o
 obj-$(CONFIG_DMABUF_HEAPS)	+= heaps/
 obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
new file mode 100644
index 000000000000..711be125428c
--- /dev/null
+++ b/drivers/dma-buf/dma-fence-unwrap.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * dma-fence-util: misc functions for dma_fence objects
+ *
+ * Copyright (C) 2022 Advanced Micro Devices, Inc.
+ * Authors:
+ *	Christian König <christian.koenig@amd.com>
+ */
+
+#include <linux/dma-fence.h>
+#include <linux/dma-fence-array.h>
+#include <linux/dma-fence-chain.h>
+#include <linux/dma-fence-unwrap.h>
+
+/* Internal helper to start new array iteration, don't use directly */
+static struct dma_fence *
+__dma_fence_unwrap_array(struct dma_fence_unwrap *cursor)
+{
+	cursor->array = dma_fence_chain_contained(cursor->chain);
+	cursor->index = 0;
+	return dma_fence_array_first(cursor->array);
+}
+
+/**
+ * dma_fence_unwrap_first - return the first fence from fence containers
+ * @head: the entrypoint into the containers
+ * @cursor: current position inside the containers
+ *
+ * Unwraps potential dma_fence_chain/dma_fence_array containers and return the
+ * first fence.
+ */
+struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head,
+					 struct dma_fence_unwrap *cursor)
+{
+	cursor->chain = dma_fence_get(head);
+	return __dma_fence_unwrap_array(cursor);
+}
+EXPORT_SYMBOL_GPL(dma_fence_unwrap_first);
+
+/**
+ * dma_fence_unwrap_next - return the next fence from a fence containers
+ * @cursor: current position inside the containers
+ *
+ * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return
+ * the next fence from them.
+ */
+struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
+{
+	struct dma_fence *tmp;
+
+	++cursor->index;
+	tmp = dma_fence_array_next(cursor->array, cursor->index);
+	if (tmp)
+		return tmp;
+
+	cursor->chain = dma_fence_chain_walk(cursor->chain);
+	return __dma_fence_unwrap_array(cursor);
+}
+EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c b/drivers/dma-buf/st-dma-fence-unwrap.c
index 039f016b57be..59628add93f5 100644
--- a/drivers/dma-buf/st-dma-fence-unwrap.c
+++ b/drivers/dma-buf/st-dma-fence-unwrap.c
@@ -4,27 +4,19 @@
  * Copyright (C) 2022 Advanced Micro Devices, Inc.
  */
 
+#include <linux/dma-fence.h>
+#include <linux/dma-fence-array.h>
+#include <linux/dma-fence-chain.h>
 #include <linux/dma-fence-unwrap.h>
-#if 0
-#include <linux/kernel.h>
-#include <linux/kthread.h>
-#include <linux/mm.h>
-#include <linux/sched/signal.h>
-#include <linux/slab.h>
-#include <linux/spinlock.h>
-#include <linux/random.h>
-#endif
 
 #include "selftest.h"
 
 #define CHAIN_SZ (4 << 10)
 
-static inline struct mock_fence {
+struct mock_fence {
 	struct dma_fence base;
 	spinlock_t lock;
-} *to_mock_fence(struct dma_fence *f) {
-	return container_of(f, struct mock_fence, base);
-}
+};
 
 static const char *mock_name(struct dma_fence *f)
 {
@@ -45,7 +37,8 @@ static struct dma_fence *mock_fence(void)
 		return NULL;
 
 	spin_lock_init(&f->lock);
-	dma_fence_init(&f->base, &mock_ops, &f->lock, 0, 0);
+	dma_fence_init(&f->base, &mock_ops, &f->lock,
+		       dma_fence_context_alloc(1), 1);
 
 	return &f->base;
 }
@@ -113,7 +106,6 @@ static int sanitycheck(void *arg)
 	if (!chain)
 		return -ENOMEM;
 
-	dma_fence_signal(f);
 	dma_fence_put(chain);
 	return err;
 }
@@ -154,10 +146,10 @@ static int unwrap_array(void *arg)
 		err = -EINVAL;
 	}
 
-	dma_fence_signal(f1);
-	dma_fence_signal(f2);
+	dma_fence_put(f1);
+	dma_fence_put(f2);
 	dma_fence_put(array);
-	return 0;
+	return err;
 }
 
 static int unwrap_chain(void *arg)
@@ -196,10 +188,10 @@ static int unwrap_chain(void *arg)
 		err = -EINVAL;
 	}
 
-	dma_fence_signal(f1);
-	dma_fence_signal(f2);
+	dma_fence_put(f1);
+	dma_fence_put(f2);
 	dma_fence_put(chain);
-	return 0;
+	return err;
 }
 
 static int unwrap_chain_array(void *arg)
@@ -242,10 +234,10 @@ static int unwrap_chain_array(void *arg)
 		err = -EINVAL;
 	}
 
-	dma_fence_signal(f1);
-	dma_fence_signal(f2);
+	dma_fence_put(f1);
+	dma_fence_put(f2);
 	dma_fence_put(chain);
-	return 0;
+	return err;
 }
 
 int dma_fence_unwrap(void)
diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
index 77e335a1bcac..e7c219da4ed7 100644
--- a/include/linux/dma-fence-unwrap.h
+++ b/include/linux/dma-fence-unwrap.h
@@ -1,7 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
- * fence-chain: chain fences together in a timeline
- *
  * Copyright (C) 2022 Advanced Micro Devices, Inc.
  * Authors:
  *	Christian König <christian.koenig@amd.com>
@@ -10,8 +8,7 @@
 #ifndef __LINUX_DMA_FENCE_UNWRAP_H
 #define __LINUX_DMA_FENCE_UNWRAP_H
 
-#include <linux/dma-fence-chain.h>
-#include <linux/dma-fence-array.h>
+struct dma_fence;
 
 /**
  * struct dma_fence_unwrap - cursor into the container structure
@@ -33,50 +30,9 @@ struct dma_fence_unwrap {
 	unsigned int index;
 };
 
-/* Internal helper to start new array iteration, don't use directly */
-static inline struct dma_fence *
-__dma_fence_unwrap_array(struct dma_fence_unwrap * cursor)
-{
-	cursor->array = dma_fence_chain_contained(cursor->chain);
-	cursor->index = 0;
-	return dma_fence_array_first(cursor->array);
-}
-
-/**
- * dma_fence_unwrap_first - return the first fence from fence containers
- * @head: the entrypoint into the containers
- * @cursor: current position inside the containers
- *
- * Unwraps potential dma_fence_chain/dma_fence_array containers and return the
- * first fence.
- */
-static inline struct dma_fence *
-dma_fence_unwrap_first(struct dma_fence *head, struct dma_fence_unwrap *cursor)
-{
-	cursor->chain = dma_fence_get(head);
-	return __dma_fence_unwrap_array(cursor);
-}
-
-/**
- * dma_fence_unwrap_next - return the next fence from a fence containers
- * @cursor: current position inside the containers
- *
- * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return
- * the next fence from them.
- */
-static inline struct dma_fence *
-dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
-{
-	struct dma_fence *tmp;
-
-	++cursor->index;
-	tmp = dma_fence_array_next(cursor->array, cursor->index);
-	if (tmp)
-		return tmp;
-
-	cursor->chain = dma_fence_chain_walk(cursor->chain);
-	return __dma_fence_unwrap_array(cursor);
-}
+struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head,
+					 struct dma_fence_unwrap *cursor);
+struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
 
 /**
  * dma_fence_unwrap_for_each - iterate over all fences in containers
-- 
2.25.1

[PATCH 3/3] dma-buf: generalize fence merging

[Christian König]

Introduce a dma_fence_merge() macro which allows to unwrap fences which
potentially can be containers as well and then merge them back together
into a flat dma_fence_array.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/dma-fence-unwrap.c    |  95 ++++++++++++++++++++
 drivers/dma-buf/st-dma-fence-unwrap.c |  47 ++++++++++
 drivers/dma-buf/sync_file.c           | 119 ++------------------------
 include/linux/dma-fence-unwrap.h      |  24 ++++++
 4 files changed, 172 insertions(+), 113 deletions(-)

diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
index 711be125428c..c9becc74896d 100644
--- a/drivers/dma-buf/dma-fence-unwrap.c
+++ b/drivers/dma-buf/dma-fence-unwrap.c
@@ -11,6 +11,7 @@
 #include <linux/dma-fence-array.h>
 #include <linux/dma-fence-chain.h>
 #include <linux/dma-fence-unwrap.h>
+#include <linux/slab.h>
 
 /* Internal helper to start new array iteration, don't use directly */
 static struct dma_fence *
@@ -57,3 +58,97 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
 	return __dma_fence_unwrap_array(cursor);
 }
 EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
+
+/* Implementation for the dma_fence_merge() marco, don't use directly */
+struct dma_fence *__dma_fence_merge(unsigned int num_fences,
+				    struct dma_fence **fences,
+				    struct dma_fence_unwrap *iter)
+{
+	struct dma_fence_array *result;
+	struct dma_fence *tmp, **array;
+	unsigned int i, count;
+
+	count = 0;
+	for (i = 0; i < num_fences; ++i) {
+		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i])
+			if (!dma_fence_is_signaled(tmp))
+				++count;
+	}
+
+	if (count == 0)
+		return dma_fence_get_stub();
+
+	if (count > INT_MAX)
+		return NULL;
+
+	array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
+	if (!array)
+		return NULL;
+
+	/*
+	 * We can't guarantee that inpute fences are ordered by context, but
+	 * it is still quite likely when this function is used multiple times.
+	 * So attempt to order the fences by context as we pass over them and
+	 * merge fences with the same context.
+	 */
+	for (i = 0; i < num_fences; ++i)
+		fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]);
+
+	count = 0;
+	do {
+		unsigned int sel;
+
+restart:
+		tmp = NULL;
+		for (i = 0; i < num_fences; ++i) {
+			struct dma_fence *next = fences[i];
+
+			if (!next || dma_fence_is_signaled(next))
+				continue;
+
+			if (!tmp || tmp->context > next->context) {
+				tmp = next;
+				sel = i;
+
+			} else if (tmp->context < next->context) {
+				continue;
+
+			} else if (dma_fence_is_later(tmp, next)) {
+				fences[i] = dma_fence_unwrap_next(&iter[i]);
+				goto restart;
+			} else {
+				fences[sel] = dma_fence_unwrap_next(&iter[sel]);
+				goto restart;
+			}
+		}
+
+		if (tmp) {
+			array[count++] = dma_fence_get(tmp);
+			fences[sel] = dma_fence_unwrap_next(&iter[sel]);
+		}
+	} while (tmp);
+
+	if (count == 0) {
+		tmp = dma_fence_get_stub();
+		goto return_tmp;
+	}
+
+	if (count == 1) {
+		tmp = array[0];
+		goto return_tmp;
+	}
+
+	result = dma_fence_array_create(count, array,
+					dma_fence_context_alloc(1),
+					1, false);
+	if (!result) {
+		tmp = NULL;
+		goto return_tmp;
+	}
+	return &result->base;
+
+return_tmp:
+	kfree(array);
+	return tmp;
+}
+EXPORT_SYMBOL_GPL(__dma_fence_merge);
diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c b/drivers/dma-buf/st-dma-fence-unwrap.c
index 59628add93f5..23ab134417ed 100644
--- a/drivers/dma-buf/st-dma-fence-unwrap.c
+++ b/drivers/dma-buf/st-dma-fence-unwrap.c
@@ -240,6 +240,52 @@ static int unwrap_chain_array(void *arg)
 	return err;
 }
 
+static int unwrap_merge(void *arg)
+{
+	struct dma_fence *fence, *f1, *f2, *f3;
+	struct dma_fence_unwrap iter;
+	int err = 0;
+
+	f1 = mock_fence();
+	if (!f1)
+		return -ENOMEM;
+
+	f2 = mock_fence();
+	if (!f2) {
+		err = -ENOMEM;
+		goto error_put_f1;
+	}
+
+	f3 = dma_fence_merge(f1, f2);
+	if (!f3) {
+		err = -ENOMEM;
+		goto error_put_f2;
+	}
+
+	dma_fence_unwrap_for_each(fence, &iter, f3) {
+		if (fence == f1) {
+			f1 = NULL;
+		} else if (fence == f2) {
+			f2 = NULL;
+		} else {
+			pr_err("Unexpected fence!\n");
+			err = -EINVAL;
+		}
+	}
+
+	if (f1 || f2) {
+		pr_err("Not all fences seen!\n");
+		err = -EINVAL;
+	}
+
+	dma_fence_put(f3);
+error_put_f2:
+	dma_fence_put(f2);
+error_put_f1:
+	dma_fence_put(f1);
+	return err;
+}
+
 int dma_fence_unwrap(void)
 {
 	static const struct subtest tests[] = {
@@ -247,6 +293,7 @@ int dma_fence_unwrap(void)
 		SUBTEST(unwrap_array),
 		SUBTEST(unwrap_chain),
 		SUBTEST(unwrap_chain_array),
+		SUBTEST(unwrap_merge),
 	};
 
 	return subtests(tests, NULL);
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 0fe564539166..fe149d7e3ce2 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -146,50 +146,6 @@ char *sync_file_get_name(struct sync_file *sync_file, char *buf, int len)
 	return buf;
 }
 
-static int sync_file_set_fence(struct sync_file *sync_file,
-			       struct dma_fence **fences, int num_fences)
-{
-	struct dma_fence_array *array;
-
-	/*
-	 * The reference for the fences in the new sync_file and held
-	 * in add_fence() during the merge procedure, so for num_fences == 1
-	 * we already own a new reference to the fence. For num_fence > 1
-	 * we own the reference of the dma_fence_array creation.
-	 */
-
-	if (num_fences == 0) {
-		sync_file->fence = dma_fence_get_stub();
-		kfree(fences);
-
-	} else if (num_fences == 1) {
-		sync_file->fence = fences[0];
-		kfree(fences);
-
-	} else {
-		array = dma_fence_array_create(num_fences, fences,
-					       dma_fence_context_alloc(1),
-					       1, false);
-		if (!array)
-			return -ENOMEM;
-
-		sync_file->fence = &array->base;
-	}
-
-	return 0;
-}
-
-static void add_fence(struct dma_fence **fences,
-		      int *i, struct dma_fence *fence)
-{
-	fences[*i] = fence;
-
-	if (!dma_fence_is_signaled(fence)) {
-		dma_fence_get(fence);
-		(*i)++;
-	}
-}
-
 /**
  * sync_file_merge() - merge two sync_files
  * @name:	name of new fence
@@ -203,84 +159,21 @@ static void add_fence(struct dma_fence **fences,
 static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 					 struct sync_file *b)
 {
-	struct dma_fence *a_fence, *b_fence, **fences;
-	struct dma_fence_unwrap a_iter, b_iter;
-	unsigned int index, num_fences;
 	struct sync_file *sync_file;
+	struct dma_fence *fence;
 
 	sync_file = sync_file_alloc();
 	if (!sync_file)
 		return NULL;
 
-	num_fences = 0;
-	dma_fence_unwrap_for_each(a_fence, &a_iter, a->fence)
-		++num_fences;
-	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
-		++num_fences;
-
-	if (num_fences > INT_MAX)
-		goto err_free_sync_file;
-
-	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
-	if (!fences)
-		goto err_free_sync_file;
-
-	/*
-	 * We can't guarantee that fences in both a and b are ordered, but it is
-	 * still quite likely.
-	 *
-	 * So attempt to order the fences as we pass over them and merge fences
-	 * with the same context.
-	 */
-
-	index = 0;
-	for (a_fence = dma_fence_unwrap_first(a->fence, &a_iter),
-	     b_fence = dma_fence_unwrap_first(b->fence, &b_iter);
-	     a_fence || b_fence; ) {
-
-		if (!b_fence) {
-			add_fence(fences, &index, a_fence);
-			a_fence = dma_fence_unwrap_next(&a_iter);
-
-		} else if (!a_fence) {
-			add_fence(fences, &index, b_fence);
-			b_fence = dma_fence_unwrap_next(&b_iter);
-
-		} else if (a_fence->context < b_fence->context) {
-			add_fence(fences, &index, a_fence);
-			a_fence = dma_fence_unwrap_next(&a_iter);
-
-		} else if (b_fence->context < a_fence->context) {
-			add_fence(fences, &index, b_fence);
-			b_fence = dma_fence_unwrap_next(&b_iter);
-
-		} else if (__dma_fence_is_later(a_fence->seqno, b_fence->seqno,
-						a_fence->ops)) {
-			add_fence(fences, &index, a_fence);
-			a_fence = dma_fence_unwrap_next(&a_iter);
-			b_fence = dma_fence_unwrap_next(&b_iter);
-
-		} else {
-			add_fence(fences, &index, b_fence);
-			a_fence = dma_fence_unwrap_next(&a_iter);
-			b_fence = dma_fence_unwrap_next(&b_iter);
-		}
+	fence = dma_fence_merge(a->fence, b->fence);
+	if (!fence) {
+		fput(sync_file->file);
+		return NULL;
 	}
-
-	if (sync_file_set_fence(sync_file, fences, index) < 0)
-		goto err_put_fences;
-
+	sync_file->fence = fence;
 	strlcpy(sync_file->user_name, name, sizeof(sync_file->user_name));
 	return sync_file;
-
-err_put_fences:
-	while (index)
-		dma_fence_put(fences[--index]);
-	kfree(fences);
-
-err_free_sync_file:
-	fput(sync_file->file);
-	return NULL;
 }
 
 static int sync_file_release(struct inode *inode, struct file *file)
diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
index e7c219da4ed7..7c0fab318301 100644
--- a/include/linux/dma-fence-unwrap.h
+++ b/include/linux/dma-fence-unwrap.h
@@ -48,4 +48,28 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
 	for (fence = dma_fence_unwrap_first(head, cursor); fence;	\
 	     fence = dma_fence_unwrap_next(cursor))
 
+struct dma_fence *__dma_fence_merge(unsigned int num_fences,
+				    struct dma_fence **fences,
+				    struct dma_fence_unwrap *cursors);
+
+/**
+ * dma_fence_merge - unwrap and merge fences
+ *
+ * All fences given as parameters are unwrapped and merged back together as flat
+ * dma_fence_array. Useful if multiple containers need to be merged together.
+ *
+ * Implemented as a macro to allocate the necessary arrays on the stack and
+ * account the stack frame size to the caller.
+ *
+ * Returns NULL on memory allocation failure, a dma_fence object representing
+ * all the given fences otherwise.
+ */
+#define dma_fence_merge(...)					\
+	({							\
+		struct dma_fence *__f[] = { __VA_ARGS__ };	\
+		struct dma_fence_unwrap __c[ARRAY_SIZE(__f)];	\
+								\
+		__dma_fence_merge(ARRAY_SIZE(__f), __f, __c);	\
+	})
+
 #endif
-- 
2.25.1

Re: [PATCH 1/3] dma-buf/sync_file: cleanup fence merging a bit

[Daniel Vetter]

On Tue, Apr 26, 2022 at 02:46:35PM +0200, Christian König wrote:
> krealloc_array() ignores attempts to reduce the array size, so the attempt
> to save memory is completely pointless here.
> 
> Also move testing for the no fence case into sync_file_set_fence(), this
> way we don't even touch the fence array when we don't have any fences.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/dma-buf/sync_file.c | 21 +++++++--------------
>  1 file changed, 7 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index 514d213261df..0fe564539166 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -157,9 +157,15 @@ static int sync_file_set_fence(struct sync_file *sync_file,
>  	 * we already own a new reference to the fence. For num_fence > 1
>  	 * we own the reference of the dma_fence_array creation.
>  	 */
> -	if (num_fences == 1) {
> +
> +	if (num_fences == 0) {
> +		sync_file->fence = dma_fence_get_stub();
> +		kfree(fences);
> +
> +	} else if (num_fences == 1) {
>  		sync_file->fence = fences[0];
>  		kfree(fences);
> +
>  	} else {
>  		array = dma_fence_array_create(num_fences, fences,
>  					       dma_fence_context_alloc(1),
> @@ -261,19 +267,6 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>  		}
>  	}
>  
> -	if (index == 0)
> -		fences[index++] = dma_fence_get_stub();
> -
> -	if (num_fences > index) {
> -		struct dma_fence **tmp;
> -
> -		/* Keep going even when reducing the size failed */
> -		tmp = krealloc_array(fences, index, sizeof(*fences),
> -				     GFP_KERNEL);
> -		if (tmp)
> -			fences = tmp;
> -	}
> -
>  	if (sync_file_set_fence(sync_file, fences, index) < 0)
>  		goto err_put_fences;
>  
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH 2/3] dma-buf: cleanup dma_fence_unwrap implementation and selftest

[Daniel Vetter]

On Tue, Apr 26, 2022 at 02:46:36PM +0200, Christian König wrote:
> Move the code from the inline functions into exported functions.
> 
> While at it also cleanup the the selftests, fix the error handling,
> remove unused functions and stop leaking memory in failed tests.

Can you split this out? At least I'm not seeing why this has to be all
smashed into one patch.
-Daniel

> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/Makefile              |  2 +-
>  drivers/dma-buf/dma-fence-unwrap.c    | 59 +++++++++++++++++++++++++++
>  drivers/dma-buf/st-dma-fence-unwrap.c | 40 ++++++++----------
>  include/linux/dma-fence-unwrap.h      | 52 ++---------------------
>  4 files changed, 80 insertions(+), 73 deletions(-)
>  create mode 100644 drivers/dma-buf/dma-fence-unwrap.c
> 
> diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
> index 4c9eb53ba3f8..70ec901edf2c 100644
> --- a/drivers/dma-buf/Makefile
> +++ b/drivers/dma-buf/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
> -	 dma-resv.o
> +	 dma-fence-unwrap.o dma-resv.o
>  obj-$(CONFIG_DMABUF_HEAPS)	+= dma-heap.o
>  obj-$(CONFIG_DMABUF_HEAPS)	+= heaps/
>  obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
> diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
> new file mode 100644
> index 000000000000..711be125428c
> --- /dev/null
> +++ b/drivers/dma-buf/dma-fence-unwrap.c
> @@ -0,0 +1,59 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * dma-fence-util: misc functions for dma_fence objects
> + *
> + * Copyright (C) 2022 Advanced Micro Devices, Inc.
> + * Authors:
> + *	Christian König <christian.koenig@amd.com>
> + */
> +
> +#include <linux/dma-fence.h>
> +#include <linux/dma-fence-array.h>
> +#include <linux/dma-fence-chain.h>
> +#include <linux/dma-fence-unwrap.h>
> +
> +/* Internal helper to start new array iteration, don't use directly */
> +static struct dma_fence *
> +__dma_fence_unwrap_array(struct dma_fence_unwrap *cursor)
> +{
> +	cursor->array = dma_fence_chain_contained(cursor->chain);
> +	cursor->index = 0;
> +	return dma_fence_array_first(cursor->array);
> +}
> +
> +/**
> + * dma_fence_unwrap_first - return the first fence from fence containers
> + * @head: the entrypoint into the containers
> + * @cursor: current position inside the containers
> + *
> + * Unwraps potential dma_fence_chain/dma_fence_array containers and return the
> + * first fence.
> + */
> +struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head,
> +					 struct dma_fence_unwrap *cursor)
> +{
> +	cursor->chain = dma_fence_get(head);
> +	return __dma_fence_unwrap_array(cursor);
> +}
> +EXPORT_SYMBOL_GPL(dma_fence_unwrap_first);
> +
> +/**
> + * dma_fence_unwrap_next - return the next fence from a fence containers
> + * @cursor: current position inside the containers
> + *
> + * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return
> + * the next fence from them.
> + */
> +struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
> +{
> +	struct dma_fence *tmp;
> +
> +	++cursor->index;
> +	tmp = dma_fence_array_next(cursor->array, cursor->index);
> +	if (tmp)
> +		return tmp;
> +
> +	cursor->chain = dma_fence_chain_walk(cursor->chain);
> +	return __dma_fence_unwrap_array(cursor);
> +}
> +EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
> diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c b/drivers/dma-buf/st-dma-fence-unwrap.c
> index 039f016b57be..59628add93f5 100644
> --- a/drivers/dma-buf/st-dma-fence-unwrap.c
> +++ b/drivers/dma-buf/st-dma-fence-unwrap.c
> @@ -4,27 +4,19 @@
>   * Copyright (C) 2022 Advanced Micro Devices, Inc.
>   */
>  
> +#include <linux/dma-fence.h>
> +#include <linux/dma-fence-array.h>
> +#include <linux/dma-fence-chain.h>
>  #include <linux/dma-fence-unwrap.h>
> -#if 0
> -#include <linux/kernel.h>
> -#include <linux/kthread.h>
> -#include <linux/mm.h>
> -#include <linux/sched/signal.h>
> -#include <linux/slab.h>
> -#include <linux/spinlock.h>
> -#include <linux/random.h>
> -#endif
>  
>  #include "selftest.h"
>  
>  #define CHAIN_SZ (4 << 10)
>  
> -static inline struct mock_fence {
> +struct mock_fence {
>  	struct dma_fence base;
>  	spinlock_t lock;
> -} *to_mock_fence(struct dma_fence *f) {
> -	return container_of(f, struct mock_fence, base);
> -}
> +};
>  
>  static const char *mock_name(struct dma_fence *f)
>  {
> @@ -45,7 +37,8 @@ static struct dma_fence *mock_fence(void)
>  		return NULL;
>  
>  	spin_lock_init(&f->lock);
> -	dma_fence_init(&f->base, &mock_ops, &f->lock, 0, 0);
> +	dma_fence_init(&f->base, &mock_ops, &f->lock,
> +		       dma_fence_context_alloc(1), 1);
>  
>  	return &f->base;
>  }
> @@ -113,7 +106,6 @@ static int sanitycheck(void *arg)
>  	if (!chain)
>  		return -ENOMEM;
>  
> -	dma_fence_signal(f);
>  	dma_fence_put(chain);
>  	return err;
>  }
> @@ -154,10 +146,10 @@ static int unwrap_array(void *arg)
>  		err = -EINVAL;
>  	}
>  
> -	dma_fence_signal(f1);
> -	dma_fence_signal(f2);
> +	dma_fence_put(f1);
> +	dma_fence_put(f2);
>  	dma_fence_put(array);
> -	return 0;
> +	return err;
>  }
>  
>  static int unwrap_chain(void *arg)
> @@ -196,10 +188,10 @@ static int unwrap_chain(void *arg)
>  		err = -EINVAL;
>  	}
>  
> -	dma_fence_signal(f1);
> -	dma_fence_signal(f2);
> +	dma_fence_put(f1);
> +	dma_fence_put(f2);
>  	dma_fence_put(chain);
> -	return 0;
> +	return err;
>  }
>  
>  static int unwrap_chain_array(void *arg)
> @@ -242,10 +234,10 @@ static int unwrap_chain_array(void *arg)
>  		err = -EINVAL;
>  	}
>  
> -	dma_fence_signal(f1);
> -	dma_fence_signal(f2);
> +	dma_fence_put(f1);
> +	dma_fence_put(f2);
>  	dma_fence_put(chain);
> -	return 0;
> +	return err;
>  }
>  
>  int dma_fence_unwrap(void)
> diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
> index 77e335a1bcac..e7c219da4ed7 100644
> --- a/include/linux/dma-fence-unwrap.h
> +++ b/include/linux/dma-fence-unwrap.h
> @@ -1,7 +1,5 @@
>  /* SPDX-License-Identifier: GPL-2.0-only */
>  /*
> - * fence-chain: chain fences together in a timeline
> - *
>   * Copyright (C) 2022 Advanced Micro Devices, Inc.
>   * Authors:
>   *	Christian König <christian.koenig@amd.com>
> @@ -10,8 +8,7 @@
>  #ifndef __LINUX_DMA_FENCE_UNWRAP_H
>  #define __LINUX_DMA_FENCE_UNWRAP_H
>  
> -#include <linux/dma-fence-chain.h>
> -#include <linux/dma-fence-array.h>
> +struct dma_fence;
>  
>  /**
>   * struct dma_fence_unwrap - cursor into the container structure
> @@ -33,50 +30,9 @@ struct dma_fence_unwrap {
>  	unsigned int index;
>  };
>  
> -/* Internal helper to start new array iteration, don't use directly */
> -static inline struct dma_fence *
> -__dma_fence_unwrap_array(struct dma_fence_unwrap * cursor)
> -{
> -	cursor->array = dma_fence_chain_contained(cursor->chain);
> -	cursor->index = 0;
> -	return dma_fence_array_first(cursor->array);
> -}
> -
> -/**
> - * dma_fence_unwrap_first - return the first fence from fence containers
> - * @head: the entrypoint into the containers
> - * @cursor: current position inside the containers
> - *
> - * Unwraps potential dma_fence_chain/dma_fence_array containers and return the
> - * first fence.
> - */
> -static inline struct dma_fence *
> -dma_fence_unwrap_first(struct dma_fence *head, struct dma_fence_unwrap *cursor)
> -{
> -	cursor->chain = dma_fence_get(head);
> -	return __dma_fence_unwrap_array(cursor);
> -}
> -
> -/**
> - * dma_fence_unwrap_next - return the next fence from a fence containers
> - * @cursor: current position inside the containers
> - *
> - * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return
> - * the next fence from them.
> - */
> -static inline struct dma_fence *
> -dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
> -{
> -	struct dma_fence *tmp;
> -
> -	++cursor->index;
> -	tmp = dma_fence_array_next(cursor->array, cursor->index);
> -	if (tmp)
> -		return tmp;
> -
> -	cursor->chain = dma_fence_chain_walk(cursor->chain);
> -	return __dma_fence_unwrap_array(cursor);
> -}
> +struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head,
> +					 struct dma_fence_unwrap *cursor);
> +struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
>  
>  /**
>   * dma_fence_unwrap_for_each - iterate over all fences in containers
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH 3/3] dma-buf: generalize fence merging

[Daniel Vetter]

On Tue, Apr 26, 2022 at 02:46:37PM +0200, Christian König wrote:
> Introduce a dma_fence_merge() macro which allows to unwrap fences which
> potentially can be containers as well and then merge them back together
> into a flat dma_fence_array.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

So this is really neat (the va args macro trick especially), but I'm not
sure how much use it is with just one user. Is there like more planned?
Or is the idea to make merging consistent so that the context sorting
trick can be done consistently?
-Daniel

> ---
>  drivers/dma-buf/dma-fence-unwrap.c    |  95 ++++++++++++++++++++
>  drivers/dma-buf/st-dma-fence-unwrap.c |  47 ++++++++++
>  drivers/dma-buf/sync_file.c           | 119 ++------------------------
>  include/linux/dma-fence-unwrap.h      |  24 ++++++
>  4 files changed, 172 insertions(+), 113 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
> index 711be125428c..c9becc74896d 100644
> --- a/drivers/dma-buf/dma-fence-unwrap.c
> +++ b/drivers/dma-buf/dma-fence-unwrap.c
> @@ -11,6 +11,7 @@
>  #include <linux/dma-fence-array.h>
>  #include <linux/dma-fence-chain.h>
>  #include <linux/dma-fence-unwrap.h>
> +#include <linux/slab.h>
>  
>  /* Internal helper to start new array iteration, don't use directly */
>  static struct dma_fence *
> @@ -57,3 +58,97 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
>  	return __dma_fence_unwrap_array(cursor);
>  }
>  EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
> +
> +/* Implementation for the dma_fence_merge() marco, don't use directly */
> +struct dma_fence *__dma_fence_merge(unsigned int num_fences,
> +				    struct dma_fence **fences,
> +				    struct dma_fence_unwrap *iter)
> +{
> +	struct dma_fence_array *result;
> +	struct dma_fence *tmp, **array;
> +	unsigned int i, count;
> +
> +	count = 0;
> +	for (i = 0; i < num_fences; ++i) {
> +		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i])
> +			if (!dma_fence_is_signaled(tmp))
> +				++count;
> +	}
> +
> +	if (count == 0)
> +		return dma_fence_get_stub();
> +
> +	if (count > INT_MAX)
> +		return NULL;
> +
> +	array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
> +	if (!array)
> +		return NULL;
> +
> +	/*
> +	 * We can't guarantee that inpute fences are ordered by context, but
> +	 * it is still quite likely when this function is used multiple times.
> +	 * So attempt to order the fences by context as we pass over them and
> +	 * merge fences with the same context.
> +	 */
> +	for (i = 0; i < num_fences; ++i)
> +		fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]);
> +
> +	count = 0;
> +	do {
> +		unsigned int sel;
> +
> +restart:
> +		tmp = NULL;
> +		for (i = 0; i < num_fences; ++i) {
> +			struct dma_fence *next = fences[i];
> +
> +			if (!next || dma_fence_is_signaled(next))
> +				continue;
> +
> +			if (!tmp || tmp->context > next->context) {
> +				tmp = next;
> +				sel = i;
> +
> +			} else if (tmp->context < next->context) {
> +				continue;
> +
> +			} else if (dma_fence_is_later(tmp, next)) {
> +				fences[i] = dma_fence_unwrap_next(&iter[i]);
> +				goto restart;
> +			} else {
> +				fences[sel] = dma_fence_unwrap_next(&iter[sel]);
> +				goto restart;
> +			}
> +		}
> +
> +		if (tmp) {
> +			array[count++] = dma_fence_get(tmp);
> +			fences[sel] = dma_fence_unwrap_next(&iter[sel]);
> +		}
> +	} while (tmp);
> +
> +	if (count == 0) {
> +		tmp = dma_fence_get_stub();
> +		goto return_tmp;
> +	}
> +
> +	if (count == 1) {
> +		tmp = array[0];
> +		goto return_tmp;
> +	}
> +
> +	result = dma_fence_array_create(count, array,
> +					dma_fence_context_alloc(1),
> +					1, false);
> +	if (!result) {
> +		tmp = NULL;
> +		goto return_tmp;
> +	}
> +	return &result->base;
> +
> +return_tmp:
> +	kfree(array);
> +	return tmp;
> +}
> +EXPORT_SYMBOL_GPL(__dma_fence_merge);
> diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c b/drivers/dma-buf/st-dma-fence-unwrap.c
> index 59628add93f5..23ab134417ed 100644
> --- a/drivers/dma-buf/st-dma-fence-unwrap.c
> +++ b/drivers/dma-buf/st-dma-fence-unwrap.c
> @@ -240,6 +240,52 @@ static int unwrap_chain_array(void *arg)
>  	return err;
>  }
>  
> +static int unwrap_merge(void *arg)
> +{
> +	struct dma_fence *fence, *f1, *f2, *f3;
> +	struct dma_fence_unwrap iter;
> +	int err = 0;
> +
> +	f1 = mock_fence();
> +	if (!f1)
> +		return -ENOMEM;
> +
> +	f2 = mock_fence();
> +	if (!f2) {
> +		err = -ENOMEM;
> +		goto error_put_f1;
> +	}
> +
> +	f3 = dma_fence_merge(f1, f2);
> +	if (!f3) {
> +		err = -ENOMEM;
> +		goto error_put_f2;
> +	}
> +
> +	dma_fence_unwrap_for_each(fence, &iter, f3) {
> +		if (fence == f1) {
> +			f1 = NULL;
> +		} else if (fence == f2) {
> +			f2 = NULL;
> +		} else {
> +			pr_err("Unexpected fence!\n");
> +			err = -EINVAL;
> +		}
> +	}
> +
> +	if (f1 || f2) {
> +		pr_err("Not all fences seen!\n");
> +		err = -EINVAL;
> +	}
> +
> +	dma_fence_put(f3);
> +error_put_f2:
> +	dma_fence_put(f2);
> +error_put_f1:
> +	dma_fence_put(f1);
> +	return err;
> +}
> +
>  int dma_fence_unwrap(void)
>  {
>  	static const struct subtest tests[] = {
> @@ -247,6 +293,7 @@ int dma_fence_unwrap(void)
>  		SUBTEST(unwrap_array),
>  		SUBTEST(unwrap_chain),
>  		SUBTEST(unwrap_chain_array),
> +		SUBTEST(unwrap_merge),
>  	};
>  
>  	return subtests(tests, NULL);
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index 0fe564539166..fe149d7e3ce2 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -146,50 +146,6 @@ char *sync_file_get_name(struct sync_file *sync_file, char *buf, int len)
>  	return buf;
>  }
>  
> -static int sync_file_set_fence(struct sync_file *sync_file,
> -			       struct dma_fence **fences, int num_fences)
> -{
> -	struct dma_fence_array *array;
> -
> -	/*
> -	 * The reference for the fences in the new sync_file and held
> -	 * in add_fence() during the merge procedure, so for num_fences == 1
> -	 * we already own a new reference to the fence. For num_fence > 1
> -	 * we own the reference of the dma_fence_array creation.
> -	 */
> -
> -	if (num_fences == 0) {
> -		sync_file->fence = dma_fence_get_stub();
> -		kfree(fences);
> -
> -	} else if (num_fences == 1) {
> -		sync_file->fence = fences[0];
> -		kfree(fences);
> -
> -	} else {
> -		array = dma_fence_array_create(num_fences, fences,
> -					       dma_fence_context_alloc(1),
> -					       1, false);
> -		if (!array)
> -			return -ENOMEM;
> -
> -		sync_file->fence = &array->base;
> -	}
> -
> -	return 0;
> -}
> -
> -static void add_fence(struct dma_fence **fences,
> -		      int *i, struct dma_fence *fence)
> -{
> -	fences[*i] = fence;
> -
> -	if (!dma_fence_is_signaled(fence)) {
> -		dma_fence_get(fence);
> -		(*i)++;
> -	}
> -}
> -
>  /**
>   * sync_file_merge() - merge two sync_files
>   * @name:	name of new fence
> @@ -203,84 +159,21 @@ static void add_fence(struct dma_fence **fences,
>  static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>  					 struct sync_file *b)
>  {
> -	struct dma_fence *a_fence, *b_fence, **fences;
> -	struct dma_fence_unwrap a_iter, b_iter;
> -	unsigned int index, num_fences;
>  	struct sync_file *sync_file;
> +	struct dma_fence *fence;
>  
>  	sync_file = sync_file_alloc();
>  	if (!sync_file)
>  		return NULL;
>  
> -	num_fences = 0;
> -	dma_fence_unwrap_for_each(a_fence, &a_iter, a->fence)
> -		++num_fences;
> -	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
> -		++num_fences;
> -
> -	if (num_fences > INT_MAX)
> -		goto err_free_sync_file;
> -
> -	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
> -	if (!fences)
> -		goto err_free_sync_file;
> -
> -	/*
> -	 * We can't guarantee that fences in both a and b are ordered, but it is
> -	 * still quite likely.
> -	 *
> -	 * So attempt to order the fences as we pass over them and merge fences
> -	 * with the same context.
> -	 */
> -
> -	index = 0;
> -	for (a_fence = dma_fence_unwrap_first(a->fence, &a_iter),
> -	     b_fence = dma_fence_unwrap_first(b->fence, &b_iter);
> -	     a_fence || b_fence; ) {
> -
> -		if (!b_fence) {
> -			add_fence(fences, &index, a_fence);
> -			a_fence = dma_fence_unwrap_next(&a_iter);
> -
> -		} else if (!a_fence) {
> -			add_fence(fences, &index, b_fence);
> -			b_fence = dma_fence_unwrap_next(&b_iter);
> -
> -		} else if (a_fence->context < b_fence->context) {
> -			add_fence(fences, &index, a_fence);
> -			a_fence = dma_fence_unwrap_next(&a_iter);
> -
> -		} else if (b_fence->context < a_fence->context) {
> -			add_fence(fences, &index, b_fence);
> -			b_fence = dma_fence_unwrap_next(&b_iter);
> -
> -		} else if (__dma_fence_is_later(a_fence->seqno, b_fence->seqno,
> -						a_fence->ops)) {
> -			add_fence(fences, &index, a_fence);
> -			a_fence = dma_fence_unwrap_next(&a_iter);
> -			b_fence = dma_fence_unwrap_next(&b_iter);
> -
> -		} else {
> -			add_fence(fences, &index, b_fence);
> -			a_fence = dma_fence_unwrap_next(&a_iter);
> -			b_fence = dma_fence_unwrap_next(&b_iter);
> -		}
> +	fence = dma_fence_merge(a->fence, b->fence);
> +	if (!fence) {
> +		fput(sync_file->file);
> +		return NULL;
>  	}
> -
> -	if (sync_file_set_fence(sync_file, fences, index) < 0)
> -		goto err_put_fences;
> -
> +	sync_file->fence = fence;
>  	strlcpy(sync_file->user_name, name, sizeof(sync_file->user_name));
>  	return sync_file;
> -
> -err_put_fences:
> -	while (index)
> -		dma_fence_put(fences[--index]);
> -	kfree(fences);
> -
> -err_free_sync_file:
> -	fput(sync_file->file);
> -	return NULL;
>  }
>  
>  static int sync_file_release(struct inode *inode, struct file *file)
> diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
> index e7c219da4ed7..7c0fab318301 100644
> --- a/include/linux/dma-fence-unwrap.h
> +++ b/include/linux/dma-fence-unwrap.h
> @@ -48,4 +48,28 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
>  	for (fence = dma_fence_unwrap_first(head, cursor); fence;	\
>  	     fence = dma_fence_unwrap_next(cursor))
>  
> +struct dma_fence *__dma_fence_merge(unsigned int num_fences,
> +				    struct dma_fence **fences,
> +				    struct dma_fence_unwrap *cursors);
> +
> +/**
> + * dma_fence_merge - unwrap and merge fences
> + *
> + * All fences given as parameters are unwrapped and merged back together as flat
> + * dma_fence_array. Useful if multiple containers need to be merged together.
> + *
> + * Implemented as a macro to allocate the necessary arrays on the stack and
> + * account the stack frame size to the caller.
> + *
> + * Returns NULL on memory allocation failure, a dma_fence object representing
> + * all the given fences otherwise.
> + */
> +#define dma_fence_merge(...)					\
> +	({							\
> +		struct dma_fence *__f[] = { __VA_ARGS__ };	\
> +		struct dma_fence_unwrap __c[ARRAY_SIZE(__f)];	\
> +								\
> +		__dma_fence_merge(ARRAY_SIZE(__f), __f, __c);	\
> +	})
> +
>  #endif
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH 3/3] dma-buf: generalize fence merging

[Christian König]

Am 04.05.22 um 10:43 schrieb Daniel Vetter:
> On Tue, Apr 26, 2022 at 02:46:37PM +0200, Christian König wrote:
>> Introduce a dma_fence_merge() macro which allows to unwrap fences which
>> potentially can be containers as well and then merge them back together
>> into a flat dma_fence_array.
>>
>> Signed-off-by: Christian König <christian.koenig@amd.com>
> So this is really neat (the va args macro trick especially), but I'm not
> sure how much use it is with just one user. Is there like more planned?

We have another potential user of this in drm_syncobj_flatten_chain() 
and at least another potential cases in amdgpu come to my mind.

I just wanted to double check the general implementation before I start 
to use this more widely.

> Or is the idea to make merging consistent so that the context sorting
> trick can be done consistently?

The context sorting trick is just a nice to have optimization. My main 
intention here is to have an utility function for flattening things out 
I can point people to which does the job and works reliable in all cases.

Christian.

> -Daniel
>
>> ---
>>   drivers/dma-buf/dma-fence-unwrap.c    |  95 ++++++++++++++++++++
>>   drivers/dma-buf/st-dma-fence-unwrap.c |  47 ++++++++++
>>   drivers/dma-buf/sync_file.c           | 119 ++------------------------
>>   include/linux/dma-fence-unwrap.h      |  24 ++++++
>>   4 files changed, 172 insertions(+), 113 deletions(-)
>>
>> diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
>> index 711be125428c..c9becc74896d 100644
>> --- a/drivers/dma-buf/dma-fence-unwrap.c
>> +++ b/drivers/dma-buf/dma-fence-unwrap.c
>> @@ -11,6 +11,7 @@
>>   #include <linux/dma-fence-array.h>
>>   #include <linux/dma-fence-chain.h>
>>   #include <linux/dma-fence-unwrap.h>
>> +#include <linux/slab.h>
>>   
>>   /* Internal helper to start new array iteration, don't use directly */
>>   static struct dma_fence *
>> @@ -57,3 +58,97 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
>>   	return __dma_fence_unwrap_array(cursor);
>>   }
>>   EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
>> +
>> +/* Implementation for the dma_fence_merge() marco, don't use directly */
>> +struct dma_fence *__dma_fence_merge(unsigned int num_fences,
>> +				    struct dma_fence **fences,
>> +				    struct dma_fence_unwrap *iter)
>> +{
>> +	struct dma_fence_array *result;
>> +	struct dma_fence *tmp, **array;
>> +	unsigned int i, count;
>> +
>> +	count = 0;
>> +	for (i = 0; i < num_fences; ++i) {
>> +		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i])
>> +			if (!dma_fence_is_signaled(tmp))
>> +				++count;
>> +	}
>> +
>> +	if (count == 0)
>> +		return dma_fence_get_stub();
>> +
>> +	if (count > INT_MAX)
>> +		return NULL;
>> +
>> +	array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
>> +	if (!array)
>> +		return NULL;
>> +
>> +	/*
>> +	 * We can't guarantee that inpute fences are ordered by context, but
>> +	 * it is still quite likely when this function is used multiple times.
>> +	 * So attempt to order the fences by context as we pass over them and
>> +	 * merge fences with the same context.
>> +	 */
>> +	for (i = 0; i < num_fences; ++i)
>> +		fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]);
>> +
>> +	count = 0;
>> +	do {
>> +		unsigned int sel;
>> +
>> +restart:
>> +		tmp = NULL;
>> +		for (i = 0; i < num_fences; ++i) {
>> +			struct dma_fence *next = fences[i];
>> +
>> +			if (!next || dma_fence_is_signaled(next))
>> +				continue;
>> +
>> +			if (!tmp || tmp->context > next->context) {
>> +				tmp = next;
>> +				sel = i;
>> +
>> +			} else if (tmp->context < next->context) {
>> +				continue;
>> +
>> +			} else if (dma_fence_is_later(tmp, next)) {
>> +				fences[i] = dma_fence_unwrap_next(&iter[i]);
>> +				goto restart;
>> +			} else {
>> +				fences[sel] = dma_fence_unwrap_next(&iter[sel]);
>> +				goto restart;
>> +			}
>> +		}
>> +
>> +		if (tmp) {
>> +			array[count++] = dma_fence_get(tmp);
>> +			fences[sel] = dma_fence_unwrap_next(&iter[sel]);
>> +		}
>> +	} while (tmp);
>> +
>> +	if (count == 0) {
>> +		tmp = dma_fence_get_stub();
>> +		goto return_tmp;
>> +	}
>> +
>> +	if (count == 1) {
>> +		tmp = array[0];
>> +		goto return_tmp;
>> +	}
>> +
>> +	result = dma_fence_array_create(count, array,
>> +					dma_fence_context_alloc(1),
>> +					1, false);
>> +	if (!result) {
>> +		tmp = NULL;
>> +		goto return_tmp;
>> +	}
>> +	return &result->base;
>> +
>> +return_tmp:
>> +	kfree(array);
>> +	return tmp;
>> +}
>> +EXPORT_SYMBOL_GPL(__dma_fence_merge);
>> diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c b/drivers/dma-buf/st-dma-fence-unwrap.c
>> index 59628add93f5..23ab134417ed 100644
>> --- a/drivers/dma-buf/st-dma-fence-unwrap.c
>> +++ b/drivers/dma-buf/st-dma-fence-unwrap.c
>> @@ -240,6 +240,52 @@ static int unwrap_chain_array(void *arg)
>>   	return err;
>>   }
>>   
>> +static int unwrap_merge(void *arg)
>> +{
>> +	struct dma_fence *fence, *f1, *f2, *f3;
>> +	struct dma_fence_unwrap iter;
>> +	int err = 0;
>> +
>> +	f1 = mock_fence();
>> +	if (!f1)
>> +		return -ENOMEM;
>> +
>> +	f2 = mock_fence();
>> +	if (!f2) {
>> +		err = -ENOMEM;
>> +		goto error_put_f1;
>> +	}
>> +
>> +	f3 = dma_fence_merge(f1, f2);
>> +	if (!f3) {
>> +		err = -ENOMEM;
>> +		goto error_put_f2;
>> +	}
>> +
>> +	dma_fence_unwrap_for_each(fence, &iter, f3) {
>> +		if (fence == f1) {
>> +			f1 = NULL;
>> +		} else if (fence == f2) {
>> +			f2 = NULL;
>> +		} else {
>> +			pr_err("Unexpected fence!\n");
>> +			err = -EINVAL;
>> +		}
>> +	}
>> +
>> +	if (f1 || f2) {
>> +		pr_err("Not all fences seen!\n");
>> +		err = -EINVAL;
>> +	}
>> +
>> +	dma_fence_put(f3);
>> +error_put_f2:
>> +	dma_fence_put(f2);
>> +error_put_f1:
>> +	dma_fence_put(f1);
>> +	return err;
>> +}
>> +
>>   int dma_fence_unwrap(void)
>>   {
>>   	static const struct subtest tests[] = {
>> @@ -247,6 +293,7 @@ int dma_fence_unwrap(void)
>>   		SUBTEST(unwrap_array),
>>   		SUBTEST(unwrap_chain),
>>   		SUBTEST(unwrap_chain_array),
>> +		SUBTEST(unwrap_merge),
>>   	};
>>   
>>   	return subtests(tests, NULL);
>> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
>> index 0fe564539166..fe149d7e3ce2 100644
>> --- a/drivers/dma-buf/sync_file.c
>> +++ b/drivers/dma-buf/sync_file.c
>> @@ -146,50 +146,6 @@ char *sync_file_get_name(struct sync_file *sync_file, char *buf, int len)
>>   	return buf;
>>   }
>>   
>> -static int sync_file_set_fence(struct sync_file *sync_file,
>> -			       struct dma_fence **fences, int num_fences)
>> -{
>> -	struct dma_fence_array *array;
>> -
>> -	/*
>> -	 * The reference for the fences in the new sync_file and held
>> -	 * in add_fence() during the merge procedure, so for num_fences == 1
>> -	 * we already own a new reference to the fence. For num_fence > 1
>> -	 * we own the reference of the dma_fence_array creation.
>> -	 */
>> -
>> -	if (num_fences == 0) {
>> -		sync_file->fence = dma_fence_get_stub();
>> -		kfree(fences);
>> -
>> -	} else if (num_fences == 1) {
>> -		sync_file->fence = fences[0];
>> -		kfree(fences);
>> -
>> -	} else {
>> -		array = dma_fence_array_create(num_fences, fences,
>> -					       dma_fence_context_alloc(1),
>> -					       1, false);
>> -		if (!array)
>> -			return -ENOMEM;
>> -
>> -		sync_file->fence = &array->base;
>> -	}
>> -
>> -	return 0;
>> -}
>> -
>> -static void add_fence(struct dma_fence **fences,
>> -		      int *i, struct dma_fence *fence)
>> -{
>> -	fences[*i] = fence;
>> -
>> -	if (!dma_fence_is_signaled(fence)) {
>> -		dma_fence_get(fence);
>> -		(*i)++;
>> -	}
>> -}
>> -
>>   /**
>>    * sync_file_merge() - merge two sync_files
>>    * @name:	name of new fence
>> @@ -203,84 +159,21 @@ static void add_fence(struct dma_fence **fences,
>>   static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>>   					 struct sync_file *b)
>>   {
>> -	struct dma_fence *a_fence, *b_fence, **fences;
>> -	struct dma_fence_unwrap a_iter, b_iter;
>> -	unsigned int index, num_fences;
>>   	struct sync_file *sync_file;
>> +	struct dma_fence *fence;
>>   
>>   	sync_file = sync_file_alloc();
>>   	if (!sync_file)
>>   		return NULL;
>>   
>> -	num_fences = 0;
>> -	dma_fence_unwrap_for_each(a_fence, &a_iter, a->fence)
>> -		++num_fences;
>> -	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
>> -		++num_fences;
>> -
>> -	if (num_fences > INT_MAX)
>> -		goto err_free_sync_file;
>> -
>> -	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
>> -	if (!fences)
>> -		goto err_free_sync_file;
>> -
>> -	/*
>> -	 * We can't guarantee that fences in both a and b are ordered, but it is
>> -	 * still quite likely.
>> -	 *
>> -	 * So attempt to order the fences as we pass over them and merge fences
>> -	 * with the same context.
>> -	 */
>> -
>> -	index = 0;
>> -	for (a_fence = dma_fence_unwrap_first(a->fence, &a_iter),
>> -	     b_fence = dma_fence_unwrap_first(b->fence, &b_iter);
>> -	     a_fence || b_fence; ) {
>> -
>> -		if (!b_fence) {
>> -			add_fence(fences, &index, a_fence);
>> -			a_fence = dma_fence_unwrap_next(&a_iter);
>> -
>> -		} else if (!a_fence) {
>> -			add_fence(fences, &index, b_fence);
>> -			b_fence = dma_fence_unwrap_next(&b_iter);
>> -
>> -		} else if (a_fence->context < b_fence->context) {
>> -			add_fence(fences, &index, a_fence);
>> -			a_fence = dma_fence_unwrap_next(&a_iter);
>> -
>> -		} else if (b_fence->context < a_fence->context) {
>> -			add_fence(fences, &index, b_fence);
>> -			b_fence = dma_fence_unwrap_next(&b_iter);
>> -
>> -		} else if (__dma_fence_is_later(a_fence->seqno, b_fence->seqno,
>> -						a_fence->ops)) {
>> -			add_fence(fences, &index, a_fence);
>> -			a_fence = dma_fence_unwrap_next(&a_iter);
>> -			b_fence = dma_fence_unwrap_next(&b_iter);
>> -
>> -		} else {
>> -			add_fence(fences, &index, b_fence);
>> -			a_fence = dma_fence_unwrap_next(&a_iter);
>> -			b_fence = dma_fence_unwrap_next(&b_iter);
>> -		}
>> +	fence = dma_fence_merge(a->fence, b->fence);
>> +	if (!fence) {
>> +		fput(sync_file->file);
>> +		return NULL;
>>   	}
>> -
>> -	if (sync_file_set_fence(sync_file, fences, index) < 0)
>> -		goto err_put_fences;
>> -
>> +	sync_file->fence = fence;
>>   	strlcpy(sync_file->user_name, name, sizeof(sync_file->user_name));
>>   	return sync_file;
>> -
>> -err_put_fences:
>> -	while (index)
>> -		dma_fence_put(fences[--index]);
>> -	kfree(fences);
>> -
>> -err_free_sync_file:
>> -	fput(sync_file->file);
>> -	return NULL;
>>   }
>>   
>>   static int sync_file_release(struct inode *inode, struct file *file)
>> diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
>> index e7c219da4ed7..7c0fab318301 100644
>> --- a/include/linux/dma-fence-unwrap.h
>> +++ b/include/linux/dma-fence-unwrap.h
>> @@ -48,4 +48,28 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
>>   	for (fence = dma_fence_unwrap_first(head, cursor); fence;	\
>>   	     fence = dma_fence_unwrap_next(cursor))
>>   
>> +struct dma_fence *__dma_fence_merge(unsigned int num_fences,
>> +				    struct dma_fence **fences,
>> +				    struct dma_fence_unwrap *cursors);
>> +
>> +/**
>> + * dma_fence_merge - unwrap and merge fences
>> + *
>> + * All fences given as parameters are unwrapped and merged back together as flat
>> + * dma_fence_array. Useful if multiple containers need to be merged together.
>> + *
>> + * Implemented as a macro to allocate the necessary arrays on the stack and
>> + * account the stack frame size to the caller.
>> + *
>> + * Returns NULL on memory allocation failure, a dma_fence object representing
>> + * all the given fences otherwise.
>> + */
>> +#define dma_fence_merge(...)					\
>> +	({							\
>> +		struct dma_fence *__f[] = { __VA_ARGS__ };	\
>> +		struct dma_fence_unwrap __c[ARRAY_SIZE(__f)];	\
>> +								\
>> +		__dma_fence_merge(ARRAY_SIZE(__f), __f, __c);	\
>> +	})
>> +
>>   #endif
>> -- 
>> 2.25.1
>>

Re: [PATCH 3/3] dma-buf: generalize fence merging

[Daniel Vetter]

On Tue, Apr 26, 2022 at 02:46:37PM +0200, Christian König wrote:
> Introduce a dma_fence_merge() macro which allows to unwrap fences which
> potentially can be containers as well and then merge them back together
> into a flat dma_fence_array.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/dma-fence-unwrap.c    |  95 ++++++++++++++++++++
>  drivers/dma-buf/st-dma-fence-unwrap.c |  47 ++++++++++
>  drivers/dma-buf/sync_file.c           | 119 ++------------------------
>  include/linux/dma-fence-unwrap.h      |  24 ++++++
>  4 files changed, 172 insertions(+), 113 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
> index 711be125428c..c9becc74896d 100644
> --- a/drivers/dma-buf/dma-fence-unwrap.c
> +++ b/drivers/dma-buf/dma-fence-unwrap.c
> @@ -11,6 +11,7 @@
>  #include <linux/dma-fence-array.h>
>  #include <linux/dma-fence-chain.h>
>  #include <linux/dma-fence-unwrap.h>
> +#include <linux/slab.h>
>  
>  /* Internal helper to start new array iteration, don't use directly */
>  static struct dma_fence *
> @@ -57,3 +58,97 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
>  	return __dma_fence_unwrap_array(cursor);
>  }
>  EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
> +
> +/* Implementation for the dma_fence_merge() marco, don't use directly */
> +struct dma_fence *__dma_fence_merge(unsigned int num_fences,
> +				    struct dma_fence **fences,
> +				    struct dma_fence_unwrap *iter)
> +{
> +	struct dma_fence_array *result;
> +	struct dma_fence *tmp, **array;
> +	unsigned int i, count;
> +
> +	count = 0;
> +	for (i = 0; i < num_fences; ++i) {
> +		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i])
> +			if (!dma_fence_is_signaled(tmp))

So I realized that dma_fence_array don't filter out signalled fences, but
dma_fence_chain does. I wonder whether we shouldn't be more consistent
here and push these checks into dma_fence_unwrap for everyone, and then
also add a huge warning that every time you iterate you might get fewer
fences, since that could lead to surprises :-)

Anyway kinda orthogonal.

> +				++count;
> +	}
> +
> +	if (count == 0)
> +		return dma_fence_get_stub();
> +
> +	if (count > INT_MAX)
> +		return NULL;

If you actually want to make this secure you need to bail out when the
count goes above INT_MAX for the first time, since you might have wrapped
still. It's a bit annoying to fix though since there's no
dma_fence_unwrap_end to clean up the temp references.

> +
> +	array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
> +	if (!array)
> +		return NULL;
> +
> +	/*
> +	 * We can't guarantee that inpute fences are ordered by context, but
> +	 * it is still quite likely when this function is used multiple times.
> +	 * So attempt to order the fences by context as we pass over them and
> +	 * merge fences with the same context.
> +	 */
> +	for (i = 0; i < num_fences; ++i)
> +		fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]);

Maybe add a comment here like "Since this function is only used through
the dma_fence_merge macro we can thrash the argument array and use it as
scratch space" or something like that, I was freaked out for a bit what's
going on here :-)

> +
> +	count = 0;
> +	do {
> +		unsigned int sel;
> +
> +restart:
> +		tmp = NULL;
> +		for (i = 0; i < num_fences; ++i) {
> +			struct dma_fence *next = fences[i];
> +
> +			if (!next || dma_fence_is_signaled(next))
> +				continue;
> +
> +			if (!tmp || tmp->context > next->context) {
> +				tmp = next;
> +				sel = i;
> +
> +			} else if (tmp->context < next->context) {
> +				continue;
> +
> +			} else if (dma_fence_is_later(tmp, next)) {
> +				fences[i] = dma_fence_unwrap_next(&iter[i]);
> +				goto restart;
> +			} else {
> +				fences[sel] = dma_fence_unwrap_next(&iter[sel]);
> +				goto restart;
> +			}
> +		}
> +
> +		if (tmp) {
> +			array[count++] = dma_fence_get(tmp);
> +			fences[sel] = dma_fence_unwrap_next(&iter[sel]);
> +		}
> +	} while (tmp);
> +
> +	if (count == 0) {
> +		tmp = dma_fence_get_stub();
> +		goto return_tmp;
> +	}
> +
> +	if (count == 1) {
> +		tmp = array[0];
> +		goto return_tmp;
> +	}
> +
> +	result = dma_fence_array_create(count, array,
> +					dma_fence_context_alloc(1),
> +					1, false);
> +	if (!result) {
> +		tmp = NULL;
> +		goto return_tmp;
> +	}
> +	return &result->base;
> +
> +return_tmp:
> +	kfree(array);
> +	return tmp;
> +}
> +EXPORT_SYMBOL_GPL(__dma_fence_merge);
> diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c b/drivers/dma-buf/st-dma-fence-unwrap.c
> index 59628add93f5..23ab134417ed 100644
> --- a/drivers/dma-buf/st-dma-fence-unwrap.c
> +++ b/drivers/dma-buf/st-dma-fence-unwrap.c
> @@ -240,6 +240,52 @@ static int unwrap_chain_array(void *arg)
>  	return err;
>  }
>  
> +static int unwrap_merge(void *arg)
> +{
> +	struct dma_fence *fence, *f1, *f2, *f3;
> +	struct dma_fence_unwrap iter;
> +	int err = 0;
> +
> +	f1 = mock_fence();
> +	if (!f1)
> +		return -ENOMEM;
> +
> +	f2 = mock_fence();
> +	if (!f2) {
> +		err = -ENOMEM;
> +		goto error_put_f1;
> +	}
> +
> +	f3 = dma_fence_merge(f1, f2);
> +	if (!f3) {
> +		err = -ENOMEM;
> +		goto error_put_f2;
> +	}
> +
> +	dma_fence_unwrap_for_each(fence, &iter, f3) {
> +		if (fence == f1) {
> +			f1 = NULL;
> +		} else if (fence == f2) {
> +			f2 = NULL;
> +		} else {
> +			pr_err("Unexpected fence!\n");
> +			err = -EINVAL;
> +		}
> +	}
> +
> +	if (f1 || f2) {
> +		pr_err("Not all fences seen!\n");
> +		err = -EINVAL;
> +	}
> +
> +	dma_fence_put(f3);
> +error_put_f2:
> +	dma_fence_put(f2);
> +error_put_f1:
> +	dma_fence_put(f1);
> +	return err;
> +}

This doesn't really exercise any of the interesting cases in your merge
loop, i.e. when there's multiple fences on the same timeline from
different containters. Would be good to exercise these cases too, since it
took me a while to understand what you're doing.

> +
>  int dma_fence_unwrap(void)
>  {
>  	static const struct subtest tests[] = {
> @@ -247,6 +293,7 @@ int dma_fence_unwrap(void)
>  		SUBTEST(unwrap_array),
>  		SUBTEST(unwrap_chain),
>  		SUBTEST(unwrap_chain_array),
> +		SUBTEST(unwrap_merge),
>  	};
>  
>  	return subtests(tests, NULL);
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index 0fe564539166..fe149d7e3ce2 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -146,50 +146,6 @@ char *sync_file_get_name(struct sync_file *sync_file, char *buf, int len)
>  	return buf;
>  }
>  
> -static int sync_file_set_fence(struct sync_file *sync_file,
> -			       struct dma_fence **fences, int num_fences)
> -{
> -	struct dma_fence_array *array;
> -
> -	/*
> -	 * The reference for the fences in the new sync_file and held
> -	 * in add_fence() during the merge procedure, so for num_fences == 1
> -	 * we already own a new reference to the fence. For num_fence > 1
> -	 * we own the reference of the dma_fence_array creation.
> -	 */
> -
> -	if (num_fences == 0) {
> -		sync_file->fence = dma_fence_get_stub();
> -		kfree(fences);
> -
> -	} else if (num_fences == 1) {
> -		sync_file->fence = fences[0];
> -		kfree(fences);
> -
> -	} else {
> -		array = dma_fence_array_create(num_fences, fences,
> -					       dma_fence_context_alloc(1),
> -					       1, false);
> -		if (!array)
> -			return -ENOMEM;
> -
> -		sync_file->fence = &array->base;
> -	}
> -
> -	return 0;
> -}
> -
> -static void add_fence(struct dma_fence **fences,
> -		      int *i, struct dma_fence *fence)
> -{
> -	fences[*i] = fence;
> -
> -	if (!dma_fence_is_signaled(fence)) {
> -		dma_fence_get(fence);
> -		(*i)++;
> -	}
> -}
> -
>  /**
>   * sync_file_merge() - merge two sync_files
>   * @name:	name of new fence
> @@ -203,84 +159,21 @@ static void add_fence(struct dma_fence **fences,
>  static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>  					 struct sync_file *b)
>  {
> -	struct dma_fence *a_fence, *b_fence, **fences;
> -	struct dma_fence_unwrap a_iter, b_iter;
> -	unsigned int index, num_fences;
>  	struct sync_file *sync_file;
> +	struct dma_fence *fence;
>  
>  	sync_file = sync_file_alloc();
>  	if (!sync_file)
>  		return NULL;
>  
> -	num_fences = 0;
> -	dma_fence_unwrap_for_each(a_fence, &a_iter, a->fence)
> -		++num_fences;
> -	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
> -		++num_fences;
> -
> -	if (num_fences > INT_MAX)
> -		goto err_free_sync_file;
> -
> -	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
> -	if (!fences)
> -		goto err_free_sync_file;
> -
> -	/*
> -	 * We can't guarantee that fences in both a and b are ordered, but it is
> -	 * still quite likely.
> -	 *
> -	 * So attempt to order the fences as we pass over them and merge fences
> -	 * with the same context.
> -	 */
> -
> -	index = 0;
> -	for (a_fence = dma_fence_unwrap_first(a->fence, &a_iter),
> -	     b_fence = dma_fence_unwrap_first(b->fence, &b_iter);
> -	     a_fence || b_fence; ) {
> -
> -		if (!b_fence) {
> -			add_fence(fences, &index, a_fence);
> -			a_fence = dma_fence_unwrap_next(&a_iter);
> -
> -		} else if (!a_fence) {
> -			add_fence(fences, &index, b_fence);
> -			b_fence = dma_fence_unwrap_next(&b_iter);
> -
> -		} else if (a_fence->context < b_fence->context) {
> -			add_fence(fences, &index, a_fence);
> -			a_fence = dma_fence_unwrap_next(&a_iter);
> -
> -		} else if (b_fence->context < a_fence->context) {
> -			add_fence(fences, &index, b_fence);
> -			b_fence = dma_fence_unwrap_next(&b_iter);
> -
> -		} else if (__dma_fence_is_later(a_fence->seqno, b_fence->seqno,
> -						a_fence->ops)) {
> -			add_fence(fences, &index, a_fence);
> -			a_fence = dma_fence_unwrap_next(&a_iter);
> -			b_fence = dma_fence_unwrap_next(&b_iter);
> -
> -		} else {
> -			add_fence(fences, &index, b_fence);
> -			a_fence = dma_fence_unwrap_next(&a_iter);
> -			b_fence = dma_fence_unwrap_next(&b_iter);
> -		}
> +	fence = dma_fence_merge(a->fence, b->fence);
> +	if (!fence) {
> +		fput(sync_file->file);
> +		return NULL;
>  	}
> -
> -	if (sync_file_set_fence(sync_file, fences, index) < 0)
> -		goto err_put_fences;
> -
> +	sync_file->fence = fence;
>  	strlcpy(sync_file->user_name, name, sizeof(sync_file->user_name));
>  	return sync_file;
> -
> -err_put_fences:
> -	while (index)
> -		dma_fence_put(fences[--index]);
> -	kfree(fences);
> -
> -err_free_sync_file:
> -	fput(sync_file->file);
> -	return NULL;
>  }
>  
>  static int sync_file_release(struct inode *inode, struct file *file)
> diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
> index e7c219da4ed7..7c0fab318301 100644
> --- a/include/linux/dma-fence-unwrap.h
> +++ b/include/linux/dma-fence-unwrap.h
> @@ -48,4 +48,28 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
>  	for (fence = dma_fence_unwrap_first(head, cursor); fence;	\
>  	     fence = dma_fence_unwrap_next(cursor))
>  
> +struct dma_fence *__dma_fence_merge(unsigned int num_fences,
> +				    struct dma_fence **fences,
> +				    struct dma_fence_unwrap *cursors);
> +
> +/**
> + * dma_fence_merge - unwrap and merge fences
> + *
> + * All fences given as parameters are unwrapped and merged back together as flat
> + * dma_fence_array. Useful if multiple containers need to be merged together.
> + *
> + * Implemented as a macro to allocate the necessary arrays on the stack and
> + * account the stack frame size to the caller.
> + *
> + * Returns NULL on memory allocation failure, a dma_fence object representing
> + * all the given fences otherwise.
> + */
> +#define dma_fence_merge(...)					\
> +	({							\
> +		struct dma_fence *__f[] = { __VA_ARGS__ };	\
> +		struct dma_fence_unwrap __c[ARRAY_SIZE(__f)];	\
> +								\
> +		__dma_fence_merge(ARRAY_SIZE(__f), __f, __c);	\

This is fancy :-)

Aside from the nits lgtm and should be useful.
-Daniel

> +	})
> +
>  #endif
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch