[PATCH 1/6] dma-buf/dma-fence: Add dma_fence_test_signaled_flag()

Philipp Stanner
2025-11-26T13:20:08Z

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@igalia.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
---
drivers/dma-buf/dma-fence.c | 19 +++++++++----------
include/linux/dma-fence.h | 24 ++++++++++++++++++++++--
2 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 39e6f93dc310..25117a906846 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -372,8 +372,7 @@ int dma_fence_signal_timestamp_locked(struct dma_fence *fence,

lockdep_assert_held(fence->lock);

- if (unlikely(test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
- &fence->flags)))
+ if (unlikely(dma_fence_test_signaled_flag(fence)))
return -EINVAL;

/* Stash the cb_list before replacing it with the timestamp */
@@ -545,7 +544,7 @@ 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 +601,7 @@ 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 +665,7 @@ 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 +782,7 @@ 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 +799,7 @@ 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 +831,7 @@ 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 +1107,7 @@ 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 +1139,7 @@ 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)) {
--
2.49.0