Re: [PATCH 1/2] dma-buf: make reservation_object_copy_fences rcu save

On Thu, Sep 07, 2017 at 09:13:32AM +0200, Christian König wrote:

Ping? David can you take a look?

Alex is on vacation and that is a rather important bug fix.

Works better when you cc Gustavo/Maarten/Sumits/Chris I think, for anything dma-buf review needing. -Daniel

Thanks, Christian.

Am 04.09.2017 um 21:02 schrieb Christian König:

...

From: Christian König christian.koenig@amd.com

Stop requiring that the src reservation object is locked for this operation.

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

drivers/dma-buf/reservation.c | 56 ++++++++++++++++++++++++++++++++----------- 1 file changed, 42 insertions(+), 14 deletions(-)

diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c index dec3a81..b44d9d7 100644 --- a/drivers/dma-buf/reservation.c +++ b/drivers/dma-buf/reservation.c @@ -266,8 +266,7 @@ EXPORT_SYMBOL(reservation_object_add_excl_fence);

• @dst: the destination reservation object
• @src: the source reservation object

-* Copy all fences from src to dst. Both src->lock as well as dst-lock must be -* held. +* Copy all fences from src to dst. dst-lock must be held. */ int reservation_object_copy_fences(struct reservation_object *dst, struct reservation_object *src) @@ -277,33 +276,62 @@ int reservation_object_copy_fences(struct reservation_object *dst, size_t size; unsigned i;

• src_list = reservation_object_get_list(src);

• rcu_read_lock();
• src_list = rcu_dereference(src->fence);

+retry: if (src_list) {

• size = offsetof(typeof(*src_list),
  

• 		shared[src_list->shared_count]);
  

• unsigned shared_count = src_list->shared_count;
  

• size = offsetof(typeof(*src_list), shared[shared_count]);
  

• rcu_read_unlock();
  

• dst_list = kmalloc(size, GFP_KERNEL); if (!dst_list) return -ENOMEM;

• dst_list->shared_count = src_list->shared_count;
  

• dst_list->shared_max = src_list->shared_count;
  

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

• 	dst_list->shared[i] =
  

• 		dma_fence_get(src_list->shared[i]);
  

• rcu_read_lock();
  

• src_list = rcu_dereference(src->fence);
  

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

• 	kfree(dst_list);
  

• 	goto retry;
  

• }
  

• dst_list->shared_count = 0;
  

• dst_list->shared_max = shared_count;
  

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

• 	struct dma_fence *fence;
  

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

• 	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
  

• 		     &fence->flags))
  

• 		continue;
  

• 	if (!dma_fence_get_rcu(fence)) {
  

• 		kfree(dst_list);
  

• 		src_list = rcu_dereference(src->fence);
  

• 		goto retry;
  

• 	}
  

• 	if (dma_fence_is_signaled(fence)) {
  

• 		dma_fence_put(fence);
  

• 		continue;
  

• 	}
  

• 	dst_list->shared[dst_list->shared_count++] = fence;
  

• }
  

  } else { dst_list = NULL; }
• new = dma_fence_get_rcu_safe(&src->fence_excl);
• rcu_read_unlock();
• kfree(dst->staged); dst->staged = NULL; src_list = reservation_object_get_list(dst);

• old = reservation_object_get_excl(dst);
• new = reservation_object_get_excl(src);
• dma_fence_get(new); preempt_disable(); write_seqcount_begin(&dst->seq);

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