linux-kernel - Re: [PATCH v2 1/8] dma-buf/dma-fence: Add dma_fence_test_signaled

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Message-ID: <f220ad03-1ad2-44aa-a46c-0a638dd64d8a@amd.com>
Date: Wed, 3 Dec 2025 14:03:33 +0100
From: Christian König <christian.koenig@....com>
To: Philipp Stanner <phasta@...nel.org>,
 Sumit Semwal <sumit.semwal@...aro.org>, Gustavo Padovan
 <gustavo@...ovan.org>, Felix Kuehling <Felix.Kuehling@....com>,
 Alex Deucher <alexander.deucher@....com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, Huang Rui <ray.huang@....com>,
 Matthew Auld <matthew.auld@...el.com>,
 Matthew Brost <matthew.brost@...el.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>
Cc: linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
 intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
 Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
Subject: Re: [PATCH v2 1/8] dma-buf/dma-fence: Add
 dma_fence_test_signaled_flag()

On 12/1/25 11:50, Philipp Stanner wrote:
> The dma_fence framework checks at many places whether the signaled flag
> of a fence is already set. The code can be simplified and made more
> readable by providing a helper function for that.
> 
> Add dma_fence_test_signaled_flag(), which only checks whether a fence is
> signaled. Use it internally.
> 
> Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
> Signed-off-by: Philipp Stanner <phasta@...nel.org>

Reviewed-by: Christian König <christian.koenig@....com>

> ---
>  drivers/dma-buf/dma-fence.c | 16 ++++++++--------
>  include/linux/dma-fence.h   | 24 ++++++++++++++++++++++--
>  2 files changed, 30 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 39e6f93dc310..96d72ffc0750 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -545,7 +545,7 @@ void dma_fence_release(struct kref *kref)
>  	trace_dma_fence_destroy(fence);
>  
>  	if (!list_empty(&fence->cb_list) &&
> -	    !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> +	    !dma_fence_test_signaled_flag(fence)) {
>  		const char __rcu *timeline;
>  		const char __rcu *driver;
>  		unsigned long flags;
> @@ -602,7 +602,7 @@ static bool __dma_fence_enable_signaling(struct dma_fence *fence)
>  	was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
>  				   &fence->flags);
>  
> -	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +	if (dma_fence_test_signaled_flag(fence))
>  		return false;
>  
>  	if (!was_set && fence->ops->enable_signaling) {
> @@ -666,7 +666,7 @@ int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
>  	if (WARN_ON(!fence || !func))
>  		return -EINVAL;
>  
> -	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> +	if (dma_fence_test_signaled_flag(fence)) {
>  		INIT_LIST_HEAD(&cb->node);
>  		return -ENOENT;
>  	}
> @@ -783,7 +783,7 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
>  
>  	spin_lock_irqsave(fence->lock, flags);
>  
> -	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +	if (dma_fence_test_signaled_flag(fence))
>  		goto out;
>  
>  	if (intr && signal_pending(current)) {
> @@ -800,7 +800,7 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
>  	cb.task = current;
>  	list_add(&cb.base.node, &fence->cb_list);
>  
> -	while (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) && ret > 0) {
> +	while (!dma_fence_test_signaled_flag(fence) && ret > 0) {
>  		if (intr)
>  			__set_current_state(TASK_INTERRUPTIBLE);
>  		else
> @@ -832,7 +832,7 @@ dma_fence_test_signaled_any(struct dma_fence **fences, uint32_t count,
>  
>  	for (i = 0; i < count; ++i) {
>  		struct dma_fence *fence = fences[i];
> -		if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> +		if (dma_fence_test_signaled_flag(fence)) {
>  			if (idx)
>  				*idx = i;
>  			return true;
> @@ -1108,7 +1108,7 @@ const char __rcu *dma_fence_driver_name(struct dma_fence *fence)
>  	RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
>  			 "RCU protection is required for safe access to returned string");
>  
> -	if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +	if (!dma_fence_test_signaled_flag(fence))
>  		return fence->ops->get_driver_name(fence);
>  	else
>  		return "detached-driver";
> @@ -1140,7 +1140,7 @@ const char __rcu *dma_fence_timeline_name(struct dma_fence *fence)
>  	RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
>  			 "RCU protection is required for safe access to returned string");
>  
> -	if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +	if (!dma_fence_test_signaled_flag(fence))
>  		return fence->ops->get_timeline_name(fence);
>  	else
>  		return "signaled-timeline";
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 64639e104110..19972f5d176f 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -401,6 +401,26 @@ void dma_fence_enable_sw_signaling(struct dma_fence *fence);
>  const char __rcu *dma_fence_driver_name(struct dma_fence *fence);
>  const char __rcu *dma_fence_timeline_name(struct dma_fence *fence);
>  
> +/*
> + * dma_fence_test_signaled_flag - Only check whether a fence is signaled yet.
> + * @fence: the fence to check
> + *
> + * This function just checks whether @fence is signaled, without interacting
> + * with the fence in any way. The user must, therefore, ensure through other
> + * means that fences get signaled eventually.
> + *
> + * This function uses test_bit(), which is thread-safe. Naturally, this function
> + * should be used opportunistically; a fence could get signaled at any moment
> + * after the check is done.
> + *
> + * Return: true if signaled, false otherwise.
> + */
> +static inline bool
> +dma_fence_test_signaled_flag(struct dma_fence *fence)
> +{
> +	return test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags);
> +}
> +
>  /**
>   * dma_fence_is_signaled_locked - Return an indication if the fence
>   *                                is signaled yet.
> @@ -418,7 +438,7 @@ const char __rcu *dma_fence_timeline_name(struct dma_fence *fence);
>  static inline bool
>  dma_fence_is_signaled_locked(struct dma_fence *fence)
>  {
> -	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +	if (dma_fence_test_signaled_flag(fence))
>  		return true;
>  
>  	if (fence->ops->signaled && fence->ops->signaled(fence)) {
> @@ -448,7 +468,7 @@ dma_fence_is_signaled_locked(struct dma_fence *fence)
>  static inline bool
>  dma_fence_is_signaled(struct dma_fence *fence)
>  {
> -	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> +	if (dma_fence_test_signaled_flag(fence))
>  		return true;
>  
>  	if (fence->ops->signaled && fence->ops->signaled(fence)) {