On 13/11/2025 14:51, Christian König wrote:
When neither a release nor a wait backend ops is specified it is possible
to let the dma_fence live on independently of the module who issued it.
This makes it possible to unload drivers and only wait for all their
fences to signal.
v2: fix typo in comment
Signed-off-by: Christian König <[email protected]>
---
drivers/dma-buf/dma-fence.c | 16 ++++++++++++----
include/linux/dma-fence.h | 4 ++--
2 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index ec21be9b089a..7074347f506d 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -374,6 +374,14 @@ int dma_fence_signal_timestamp_locked(struct dma_fence
*fence,
&fence->flags)))
return -EINVAL;
+ /*
+ * When neither a release nor a wait operation is specified set the ops
+ * pointer to NULL to allow the fence structure to become independent
+ * from who originally issued it.
+ */
+ if (!fence->ops->release && !fence->ops->wait)
+ RCU_INIT_POINTER(fence->ops, NULL);
+
/* Stash the cb_list before replacing it with the timestamp */
list_replace(&fence->cb_list, &cb_list);
@@ -513,7 +521,7 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
rcu_read_lock();
ops = rcu_dereference(fence->ops);
trace_dma_fence_wait_start(fence);
- if (ops->wait) {
+ if (ops && ops->wait) {
/*
* Implementing the wait ops is deprecated and not supported for
* issuer independent fences, so it is ok to use the ops outside
@@ -578,7 +586,7 @@ void dma_fence_release(struct kref *kref)
}
ops = rcu_dereference(fence->ops);
- if (ops->release)
+ if (ops && ops->release)
ops->release(fence);
else
dma_fence_free(fence);
@@ -614,7 +622,7 @@ static bool __dma_fence_enable_signaling(struct dma_fence
*fence)
rcu_read_lock();
ops = rcu_dereference(fence->ops);
- if (!was_set && ops->enable_signaling) {
+ if (!was_set && ops && ops->enable_signaling) {
trace_dma_fence_enable_signal(fence);
if (!ops->enable_signaling(fence)) {
@@ -1000,7 +1008,7 @@ void dma_fence_set_deadline(struct dma_fence *fence,
ktime_t deadline)
rcu_read_lock();
ops = rcu_dereference(fence->ops);
- if (ops->set_deadline && !dma_fence_is_signaled(fence))
+ if (ops && ops->set_deadline && !dma_fence_is_signaled(fence))
ops->set_deadline(fence, deadline);
rcu_read_unlock();
}
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 77f07735f556..eb57bcc8712f 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -436,7 +436,7 @@ dma_fence_is_signaled_locked(struct dma_fence *fence)
rcu_read_lock();
ops = rcu_dereference(fence->ops);
- if (ops->signaled && ops->signaled(fence)) {
+ if (ops && ops->signaled && ops->signaled(fence)) {
rcu_read_unlock();
dma_fence_signal_locked(fence);
return true;
@@ -472,7 +472,7 @@ dma_fence_is_signaled(struct dma_fence *fence)
rcu_read_lock();
ops = rcu_dereference(fence->ops);
- if (ops->signaled && ops->signaled(fence)) {
+ if (ops && ops->signaled && ops->signaled(fence)) {
rcu_read_unlock();
dma_fence_signal(fence);
return true;
Reviewed-by: Tvrtko Ursulin <[email protected]>
Regards,
Tvrtko
