On 05/08/2019 10:36, Christian König wrote:
We can't free up the chain using recursion or we run into a stack overflow.
Manually free up the dangling chain nodes to avoid recursion.
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
That definitely makes sense to me, but I'm not an expert in RCU foo :/
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
I guess this deserves a
Fixes: 7bf60c52e0 ("dma-buf: add new dma_fence_chain container v7")
---
drivers/dma-buf/dma-fence-chain.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
index b5089f64be2a..44a741677d25 100644
--- a/drivers/dma-buf/dma-fence-chain.c
+++ b/drivers/dma-buf/dma-fence-chain.c
@@ -178,8 +178,30 @@ static bool dma_fence_chain_signaled(struct dma_fence *fence)
static void dma_fence_chain_release(struct dma_fence *fence)
{
struct dma_fence_chain *chain = to_dma_fence_chain(fence);
+ struct dma_fence *prev;
+
+ /* Manually unlink the chain as much as possible to avoid recursion
+ * and potential stack overflow.
+ */
+ while ((prev = rcu_dereference_protected(chain->prev, true))) {
+ struct dma_fence_chain *prev_chain;
+
+ if (kref_read(&prev->refcount) > 1)
+ break;
+
+ prev_chain = to_dma_fence_chain(prev);
+ if (!prev_chain)
+ break;
+
+ /* No need for atomic operations since we hold the last
+ * reference to prev_chain.
+ */
+ chain->prev = prev_chain->prev;
+ RCU_INIT_POINTER(prev_chain->prev, NULL);
+ dma_fence_put(prev);
+ }
+ dma_fence_put(prev);
- dma_fence_put(rcu_dereference_protected(chain->prev, true));
dma_fence_put(chain->fence);
dma_fence_free(fence);
}
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