int dma_resv_reserve_shared()

in dma-resv.c [152:214]

• 38 lines of code
• 9 McCabe index (conditional complexity)

int dma_resv_reserve_shared(struct dma_resv *obj, unsigned int num_fences)
{
	struct dma_resv_list *old, *new;
	unsigned int i, j, k, max;

	dma_resv_assert_held(obj);

	old = dma_resv_shared_list(obj);
	if (old && old->shared_max) {
		if ((old->shared_count + num_fences) <= old->shared_max)
			return 0;
		max = max(old->shared_count + num_fences, old->shared_max * 2);
	} else {
		max = max(4ul, roundup_pow_of_two(num_fences));
	}

	new = dma_resv_list_alloc(max);
	if (!new)
		return -ENOMEM;

	/*
	 * no need to bump fence refcounts, rcu_read access
	 * requires the use of kref_get_unless_zero, and the
	 * references from the old struct are carried over to
	 * the new.
	 */
	for (i = 0, j = 0, k = max; i < (old ? old->shared_count : 0); ++i) {
		struct dma_fence *fence;

		fence = rcu_dereference_protected(old->shared[i],
						  dma_resv_held(obj));
		if (dma_fence_is_signaled(fence))
			RCU_INIT_POINTER(new->shared[--k], fence);
		else
			RCU_INIT_POINTER(new->shared[j++], fence);
	}
	new->shared_count = j;

	/*
	 * We are not changing the effective set of fences here so can
	 * merely update the pointer to the new array; both existing
	 * readers and new readers will see exactly the same set of
	 * active (unsignaled) shared fences. Individual fences and the
	 * old array are protected by RCU and so will not vanish under
	 * the gaze of the rcu_read_lock() readers.
	 */
	rcu_assign_pointer(obj->fence, new);

	if (!old)
		return 0;

	/* Drop the references to the signaled fences */
	for (i = k; i < max; ++i) {
		struct dma_fence *fence;

		fence = rcu_dereference_protected(new->shared[i],
						  dma_resv_held(obj));
		dma_fence_put(fence);
	}
	kfree_rcu(old, rcu);

	return 0;
}