Re: [Linaro-mm-sig] [PATCH 03/26] dma-buf: use new iterator in dma_resv_copy_fences

On Fri, Sep 17, 2021 at 02:34:50PM +0200, Christian König wrote:

This makes the function much simpler since the complex retry logic is now handled else where.

Signed-off-by: Christian König christian.koenig@amd.com

drivers/dma-buf/dma-resv.c | 86 ++++++++++++++++---------------------- 1 file changed, 35 insertions(+), 51 deletions(-)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index a3c79a99fb44..406150dea5e4 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -426,74 +426,58 @@ EXPORT_SYMBOL_GPL(dma_resv_iter_walk); */ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src) {

• struct dma_resv_list *src_list, *dst_list;
• struct dma_fence *old, *new;
• unsigned int i;

• struct dma_resv_iter cursor;
• struct dma_resv_list *list;
• struct dma_fence *f, *excl;

dma_resv_assert_held(dst);

• rcu_read_lock();
• src_list = dma_resv_shared_list(src);

-retry:

• if (src_list) {

• unsigned int shared_count = src_list->shared_count;
  

• rcu_read_unlock();
  

• list = NULL;
• excl = NULL;

• dst_list = dma_resv_list_alloc(shared_count);
  

• if (!dst_list)
  

• 	return -ENOMEM;
  

• rcu_read_lock();
• dma_resv_iter_begin(&cursor, src, true);
• dma_resv_for_each_fence_unlocked(&cursor, f) {

• rcu_read_lock();
  

• src_list = dma_resv_shared_list(src);
  

• if (!src_list || src_list->shared_count > shared_count) {
  

• 	kfree(dst_list);
  

• 	goto retry;
  

• }
  

• if (cursor.is_first) {
  

Maybe have a wrapper for this, like dma_resv_iter_is_reset or is_first or is_restart (my preference) with some nice docs that this returns true everytime we had to restart the sequence?

Otherwise I fully agree, this is so much better with all the hairy restarting and get_rcu and test_bit shovelled away somewhere.

Either way (but I much prefer a wrapper for is_first):

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

• 	dma_resv_list_free(list);
  

• 	dma_fence_put(excl);
  

• dst_list->shared_count = 0;
  

• for (i = 0; i < src_list->shared_count; ++i) {
  

• 	struct dma_fence __rcu **dst;
  

• 	struct dma_fence *fence;
  

• 	if (cursor.fences) {
  

• 		unsigned int cnt = cursor.fences->shared_count;
  

• 	fence = rcu_dereference(src_list->shared[i]);
  

• 	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
  

• 		     &fence->flags))
  

• 		continue;
  

• 		rcu_read_unlock();
  

• 		list = dma_resv_list_alloc(cnt);
  

• 		if (!list) {
  

• 			dma_resv_iter_end(&cursor);
  

• 			return -ENOMEM;
  

• 		}
  

• 	if (!dma_fence_get_rcu(fence)) {
  

• 		dma_resv_list_free(dst_list);
  

• 		src_list = dma_resv_shared_list(src);
  

• 		goto retry;
  

• 	}
  

• 		list->shared_count = 0;
  

• 		rcu_read_lock();
  

• 	if (dma_fence_is_signaled(fence)) {
  

• 		dma_fence_put(fence);
  

• 		continue;
  

• 	} else {
  

• 		list = NULL;
  }
  

• 	dst = &dst_list->shared[dst_list->shared_count++];
  

• 	rcu_assign_pointer(*dst, fence);
  

• 	excl = NULL;
  

  }

• } else {

• dst_list = NULL;
  

• }

• new = dma_fence_get_rcu_safe(&src->fence_excl);

• dma_fence_get(f);
  

• if (dma_resv_iter_is_exclusive(&cursor))
  

• 	excl = f;
  

• else
  

• 	RCU_INIT_POINTER(list->shared[list->shared_count++], f);
  

• }
• dma_resv_iter_end(&cursor); rcu_read_unlock();

• src_list = dma_resv_shared_list(dst);
• old = dma_resv_excl_fence(dst);
• write_seqcount_begin(&dst->seq);
• /* write_seqcount_begin provides the necessary memory barrier */
• RCU_INIT_POINTER(dst->fence_excl, new);
• RCU_INIT_POINTER(dst->fence, dst_list);

• excl = rcu_replace_pointer(dst->fence_excl, excl, dma_resv_held(dst));
• list = rcu_replace_pointer(dst->fence, list, dma_resv_held(dst)); write_seqcount_end(&dst->seq);

• dma_resv_list_free(src_list);
• dma_fence_put(old);

• dma_resv_list_free(list);
• dma_fence_put(excl);

return 0; } -- 2.25.1