Re: [PATCH v19 28/40] dept: assign unique dept_key to each distinct dma fence caller

[Yunseong Kim <ysk@kzalloc.com>]

Hi Nathan,

After reading your thoughtful comments, I tested the Clang build issue
related to "indirect goto" on a v7.2 kernel with DEPT enabled:

 $ clang -v
 Debian clang version 21.1.8 (10)

 $ vng --arch arm64 --build LLVM=1 --configitem CONFIG_DEPT=y \
       --configitem CONFIG_DRM_XE=m --configitem CONFIG_ARCH_QCOM=y \
       --configitem CONFIG_DRM_MSM=m

Tested branch is here: https://github.com/yskzalloc/linux-dept/tree/dept19_v7.2

Since the update to the dma_fence_wait() usage in the 7.2 rc, Clang has no
longer reported the "indirect goto" issue.

Link: https://github.com/llvm/llvm-project/issues/138272#issuecomment-5404767476
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4e28aa8f7ee26d67a4addee6e3980f1cbf861b49
Tested-by: Yunseong Kim <yunseong.kim@est.tech>

On 06/07/2026 8:19 am, Byungchul Park wrote:
> dma fence can be used at various points in the code and it's very hard
> to distinguish dma fences between different usages.  Using a single
> dept_key for all the dma fences could trigger false positive reports.
> 
> Assign unique dept_key to each distinct dma fence wait to avoid false
> positive reports.
> 
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> ---
>  drivers/dma-buf/dma-fence.c | 18 ++++-----
>  include/linux/dma-fence.h   | 74 +++++++++++++++++++++++++++++--------
>  2 files changed, 68 insertions(+), 24 deletions(-)
> 
[snip...]
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index d4c92fd35092..3732849a30b7 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -370,8 +370,22 @@ bool dma_fence_check_and_signal_locked(struct dma_fence *fence);
>  void dma_fence_signal_locked(struct dma_fence *fence);
>  void dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
>  void dma_fence_signal_timestamp_locked(struct dma_fence *fence, ktime_t timestamp);
> -signed long dma_fence_default_wait(struct dma_fence *fence,
> +signed long __dma_fence_default_wait(struct dma_fence *fence,
>  				   bool intr, signed long timeout);
> +
> +/*
> + * Associate every caller with its own dept map.
> + */
> +#define dma_fence_default_wait(f, intr, t)				\
> +({									\
> +	signed long __ret;						\
> +									\
> +	sdt_might_sleep_start_timeout(NULL, t);				\
> +	__ret = __dma_fence_default_wait(f, intr, t);			\
> +	sdt_might_sleep_end();						\
> +	__ret;								\
> +})
> +
>  int dma_fence_add_callback(struct dma_fence *fence,
>  			   struct dma_fence_cb *cb,
>  			   dma_fence_func_t func);
> @@ -628,12 +642,37 @@ static inline ktime_t dma_fence_timestamp(struct dma_fence *fence)
>  	return fence->timestamp;
>  }
>  
> -signed long dma_fence_wait_timeout(struct dma_fence *,
> +signed long __dma_fence_wait_timeout(struct dma_fence *,
>  				   bool intr, signed long timeout);
> -signed long dma_fence_wait_any_timeout(struct dma_fence **fences,
> +signed long __dma_fence_wait_any_timeout(struct dma_fence **fences,
>  				       uint32_t count,
>  				       bool intr, signed long timeout,
>  				       uint32_t *idx);
> +/*
> + * Associate every caller with its own dept map.
> + */
> +#define dma_fence_wait_timeout(f, intr, t)				\
> +({									\
> +	signed long __ret;						\
> +									\
> +	sdt_might_sleep_start_timeout(NULL, t);				\
> +	__ret = __dma_fence_wait_timeout(f, intr, t);			\
> +	sdt_might_sleep_end();						\
> +	__ret;								\
> +})
> +
> +/*
> + * Associate every caller with its own dept map.
> + */
> +#define dma_fence_wait_any_timeout(fpp, count, intr, t, idx)		\
> +({									\
> +	signed long __ret;						\
> +									\
> +	sdt_might_sleep_start_timeout(NULL, t);				\
> +	__ret = __dma_fence_wait_any_timeout(fpp, count, intr, t, idx);	\
> +	sdt_might_sleep_end();						\
> +	__ret;								\
> +})
>  
>  /**
>   * dma_fence_wait - sleep until the fence gets signaled
> @@ -649,19 +688,24 @@ signed long dma_fence_wait_any_timeout(struct dma_fence **fences,
>   * fence might be freed before return, resulting in undefined behavior.
>   *
>   * See also dma_fence_wait_timeout() and dma_fence_wait_any_timeout().
> + *
> + * Associate every caller with its own dept map.
>   */
> -static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
> -{
> -	signed long ret;
> -
> -	/* Since dma_fence_wait_timeout cannot timeout with
> -	 * MAX_SCHEDULE_TIMEOUT, only valid return values are
> -	 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.
> -	 */
> -	ret = dma_fence_wait_timeout(fence, intr, MAX_SCHEDULE_TIMEOUT);
> -
> -	return ret < 0 ? ret : 0;
> -}
> +#define dma_fence_wait(f, intr)						\
> +({									\
> +	signed long __ret;						\
> +									\
> +	sdt_might_sleep_start_timeout(NULL, MAX_SCHEDULE_TIMEOUT);	\
> +	__ret = __dma_fence_wait_timeout(f, intr, MAX_SCHEDULE_TIMEOUT);\
> +	sdt_might_sleep_end();						\
> +									\
> +	/*								\
> +	 * Since dma_fence_wait_timeout cannot timeout with		\
> +	 * MAX_SCHEDULE_TIMEOUT, only valid return values are		\
> +	 * -ERESTARTSYS and MAX_SCHEDULE_TIMEOUT.			\
> +	 */								\
> +	__ret < 0 ? __ret : 0;						\
> +})

Thank you all! :)

Best regards,
Yunseong