Commit 541c8f24 authored by Christian König's avatar Christian König
Browse files

dma-buf: detach fence ops on signal v3 



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
v3: fix sparse rcu warnings

Signed-off-by: default avatarChristian König <christian.koenig@amd.com>
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reviewed-by: default avatarPhilipp Stanner <phasta@kernel.org>
Reviewed-by: default avatarBoris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/r/20260219160822.1529-3-christian.koenig@amd.com
parent f4cc3ab8

drivers/dma-buf/dma-fence.c

+14 −4
Original line number Diff line number Diff line
@@ -362,6 +362,7 @@ void __dma_fence_might_wait(void) 
void dma_fence_signal_timestamp_locked(struct dma_fence *fence,

				      ktime_t timestamp)

{

	const struct dma_fence_ops *ops;

	struct dma_fence_cb *cur, *tmp;

	struct list_head cb_list;
@@ -371,6 +372,15 @@ void dma_fence_signal_timestamp_locked(struct dma_fence *fence, 
				      &fence->flags)))

		return;



	/*

	 * 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.

	 */

	ops = rcu_dereference_protected(fence->ops, true);

	if (!ops->release && !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);
@@ -537,7 +547,7 @@ 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

		 * issuers of fences who need their lifetime to be independent
@@ -603,7 +613,7 @@ 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);
@@ -639,7 +649,7 @@ 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)) {
@@ -1025,7 +1035,7 @@ 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();

}

include/linux/dma-fence.h

+2 −2
Original line number Diff line number Diff line
@@ -472,7 +472,7 @@ 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;
@@ -508,7 +508,7 @@ 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;