On 2/24/26 18:55, Matthew Brost wrote:
> dma_fence_chain_enable_signaling() runs while holding the chain
> inline_lock and may add callbacks to underlying fences, which takes
> their inline_lock.
Just for the record, we have the same problem for dma_fence_chain_is_signaled().
Maybe mention that in the commit message as well for completeness.
>
> Since both locks share the same lockdep class, this valid nesting
> triggers a recursive locking warning. Assign a distinct lockdep class
> to the chain inline_lock so lockdep can correctly model the hierarchy.
Thanks a lot! I was just about to figure out how to do this.
>
> Fixes: a408c0ca0c41 ("dma-buf: use inline lock for the dma-fence-chain")
> Cc: Christian König <[email protected]>
> Cc: Tvrtko Ursulin <[email protected]>
> Cc: Philipp Stanner <[email protected]>
> Cc: Boris Brezillon <[email protected]>
> Signed-off-by: Matthew Brost <[email protected]>
Reviewed-by: Christian König <[email protected]> for both patches.
Regards,
Christian.
> ---
> drivers/dma-buf/dma-fence-chain.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-fence-chain.c
> b/drivers/dma-buf/dma-fence-chain.c
> index a707792b6025..4c2a9f2ce126 100644
> --- a/drivers/dma-buf/dma-fence-chain.c
> +++ b/drivers/dma-buf/dma-fence-chain.c
> @@ -242,6 +242,9 @@ void dma_fence_chain_init(struct dma_fence_chain *chain,
> struct dma_fence *fence,
> uint64_t seqno)
> {
> +#if IS_ENABLED(CONFIG_LOCKDEP)
> + static struct lock_class_key dma_fence_chain_lock_key;
> +#endif
> struct dma_fence_chain *prev_chain = to_dma_fence_chain(prev);
> uint64_t context;
>
> @@ -263,6 +266,20 @@ void dma_fence_chain_init(struct dma_fence_chain *chain,
> dma_fence_init64(&chain->base, &dma_fence_chain_ops, NULL,
> context, seqno);
>
> +#if IS_ENABLED(CONFIG_LOCKDEP)
> + /*
> + * dma_fence_chain_enable_signaling() is invoked while holding
> + * chain->base.inline_lock and may call dma_fence_add_callback()
> + * on the underlying fences, which takes their inline_lock.
> + *
> + * Since both locks share the same lockdep class, this legitimate
> + * nesting confuses lockdep and triggers a recursive locking
> + * warning. Assign a separate lockdep class to the chain lock
> + * to model this hierarchy correctly.
> + */
> + lockdep_set_class(&chain->base.inline_lock, &dma_fence_chain_lock_key);
> +#endif
> +
> /*
> * Chaining dma_fence_chain container together is only allowed through
> * the prev fence and not through the contained fence.
