Re: [PATCH 03/23] dma-buf: add dma_resv_get_singleton v2

[Christian König]

Daniel any more comments on this one here?

It's the prerequisite to a bunch of other patches and I would like to 
get it out of my feet.

Thanks,
Christian.

Am 21.03.22 um 14:58 schrieb Christian König:
Add a function to simplify getting a single fence for all the fences in
the dma_resv object.

v2: fix ref leak in error handling

Signed-off-by: Christian König <christian.koe...@amd.com>
---
  drivers/dma-buf/dma-resv.c | 52 ++++++++++++++++++++++++++++++++++++++
  include/linux/dma-resv.h   |  2 ++
  2 files changed, 54 insertions(+)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 5001e9b4420a..c09fd8da0c85 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -34,6 +34,7 @@
   */
  
  #include <linux/dma-resv.h>
+#include <linux/dma-fence-array.h>
  #include <linux/export.h>
  #include <linux/mm.h>
  #include <linux/sched/mm.h>
@@ -650,6 +651,57 @@ int dma_resv_get_fences(struct dma_resv *obj, bool write,
  }
  EXPORT_SYMBOL_GPL(dma_resv_get_fences);
  
+/**
+ * dma_resv_get_singleton - Get a single fence for all the fences
+ * @obj: the reservation object
+ * @write: true if we should return all fences
+ * @fence: the resulting fence
+ *
+ * Get a single fence representing all the fences inside the resv object.
+ * Returns either 0 for success or -ENOMEM.
+ *
+ * Warning: This can't be used like this when adding the fence back to the resv
+ * object since that can lead to stack corruption when finalizing the
+ * dma_fence_array.
+ */
+int dma_resv_get_singleton(struct dma_resv *obj, bool write,
+                          struct dma_fence **fence)
+{
+       struct dma_fence_array *array;
+       struct dma_fence **fences;
+       unsigned count;
+       int r;
+
+       r = dma_resv_get_fences(obj, write, &count, &fences);
+        if (r)
+               return r;
+
+       if (count == 0) {
+               *fence = NULL;
+               return 0;
+       }
+
+       if (count == 1) {
+               *fence = fences[0];
+               kfree(fences);
+               return 0;
+       }
+
+       array = dma_fence_array_create(count, fences,
+                                      dma_fence_context_alloc(1),
+                                      1, false);
+       if (!array) {
+               while (count--)
+                       dma_fence_put(fences[count]);
+               kfree(fences);
+               return -ENOMEM;
+       }
+
+       *fence = &array->base;
+       return 0;
+}
+EXPORT_SYMBOL_GPL(dma_resv_get_singleton);
+
  /**
   * dma_resv_wait_timeout - Wait on reservation's objects
   * shared and/or exclusive fences.
diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index 202cc65d0621..08512c1e215d 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -449,6 +449,8 @@ void dma_resv_replace_fences(struct dma_resv *obj, uint64_t 
context,
  void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence);
  int dma_resv_get_fences(struct dma_resv *obj, bool write,
                        unsigned int *num_fences, struct dma_fence ***fences);
+int dma_resv_get_singleton(struct dma_resv *obj, bool write,
+                          struct dma_fence **fence);
  int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src);
  long dma_resv_wait_timeout(struct dma_resv *obj, bool wait_all, bool intr,
                           unsigned long timeout);