Abstract the complexity of iterating over all the fences
in a dma_resv object.
The new loop handles the whole RCU and retry dance and
returns only fences where we can be sure we grabbed the
right one.
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/dma-buf/dma-resv.c | 63 ++++++++++++++++++++++++++++++++++++++
include/linux/dma-resv.h | 36 ++++++++++++++++++++++
2 files changed, 99 insertions(+)
diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 18dd5a6ca06c..d8da8a914b07 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -316,6 +316,69 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence)
}
EXPORT_SYMBOL(dma_resv_add_excl_fence);
+/**
+ * dma_resv_walk_unlocked - walk over fences in a dma_resv obj
+ * @obj: the dma_resv object
+ * @cursor: cursor to record the current position
+ * @all_fences: true returns also the shared fences
+ * @first: if we should start over
+ *
+ * Return all the fences in the dma_resv object which are not yet signaled.
+ * The returned fence has an extra local reference so will stay alive.
+ * If a concurrent modify is detected the whole iterator is started over again.
+ */
+struct dma_fence *dma_resv_walk_unlocked(struct dma_resv *obj,
+ struct dma_resv_cursor *cursor,
+ bool all_fences, bool first)
+{
+ struct dma_fence *fence = NULL;
+
+ do {
+ /* Drop the reference from the previous round */
+ dma_fence_put(fence);
+
+ cursor->is_first = first;
+ if (first) {
+ cursor->seq = read_seqcount_begin(&obj->seq);
+ cursor->index = -1;
+ cursor->fences = dma_resv_shared_list(obj);
+ cursor->is_exclusive = true;
+
+ fence = dma_resv_excl_fence(obj);
+ if (fence && test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
+ &fence->flags))
+ fence = NULL;
+ } else {
+ fence = NULL;
+ }
+
+ if (fence) {
+ fence = dma_fence_get_rcu(fence);
+ } else if (all_fences && cursor->fences) {
+ struct dma_resv_list *fences = cursor->fences;
+
+ cursor->is_exclusive = false;
+ while (++cursor->index < fences->shared_count) {
+ fence = rcu_dereference(fences->shared[
+ cursor->index]);
+ if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
+ &fence->flags))
+ break;
+ }
+ if (cursor->index < fences->shared_count)
+ fence = dma_fence_get_rcu(fence);
+ else
+ fence = NULL;
+ }
+
+ /* For the eventually next round */
+ first = true;
+ } while (read_seqcount_retry(&obj->seq, cursor->seq));
+
+ return fence;
+}
+EXPORT_SYMBOL_GPL(dma_resv_walk_unlocked);
+
/**
* dma_resv_copy_fences - Copy all fences from src to dst.
* @dst: the destination reservation object
diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index 562b885cf9c3..74775f2cb679 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -75,6 +75,39 @@ struct dma_resv {
struct dma_resv_list __rcu *fence;
};
+/**
+ * struct dma_resv_cursor - current position into the dma_resv fences
+ * @seq: sequence number to check
+ * @index: index into the shared fences
+ * @shared: the shared fences
+ * @is_first: true if this is the first returned fence
+ * @is_exclusive: if the current fence is the exclusive one
+ */
+struct dma_resv_cursor {
+ unsigned int seq;
+ unsigned int index;
+ struct dma_resv_list *fences;
+ bool is_first;
+ bool is_exclusive;
+};
+
+/**
+ * dma_resv_for_each_fence_unlocked - fence iterator
+ * @obj: a dma_resv object pointer
+ * @cursor: a struct dma_resv_cursor pointer
+ * @all_fences: true if all fences should be returned
+ * @fence: the current fence
+ *
+ * Iterate over the fences in a struct dma_resv object without holding the
+ * dma_resv::lock. The RCU read side lock must be hold when using this, but can
+ * be dropped and re-taken as necessary inside the loop. @all_fences controls
+ * if the shared fences are returned as well.
+ */
+#define dma_resv_for_each_fence_unlocked(obj, cursor, all_fences, fence) \
+ for (fence = dma_resv_walk_unlocked(obj, cursor, all_fences, true); \
+ fence; dma_fence_put(fence), \
+ fence = dma_resv_walk_unlocked(obj, cursor, all_fences, false))
+
#define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base)
#define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
@@ -272,6 +305,9 @@ void dma_resv_fini(struct dma_resv *obj);
int dma_resv_reserve_shared(struct dma_resv *obj, unsigned int num_fences);
void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence);
void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence);
+struct dma_fence *dma_resv_walk_unlocked(struct dma_resv *obj,
+ struct dma_resv_cursor *cursor,
+ bool first, bool all_fences);
int dma_resv_get_fences(struct dma_resv *obj, struct dma_fence **pfence_excl,
unsigned *pshared_count, struct dma_fence ***pshared);
int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src);
--
2.25.1
