From 541c8f2468b933acc5d129e84bd264923675a66e Mon Sep 17 00:00:00 2001 From: =?utf8?q?Christian=20K=C3=B6nig?= Date: Wed, 8 Oct 2025 18:12:46 +0200 Subject: [PATCH] dma-buf: detach fence ops on signal v3 MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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: Christian König Reviewed-by: Tvrtko Ursulin Reviewed-by: Philipp Stanner Reviewed-by: Boris Brezillon Link: https://lore.kernel.org/r/20260219160822.1529-3-christian.koenig@amd.com --- drivers/dma-buf/dma-fence.c | 18 ++++++++++++++---- include/linux/dma-fence.h | 4 ++-- 2 files changed, 16 insertions(+), 6 deletions(-) diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 076e6e6c75bef..3279d82ffa987 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -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(); } diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index fa3cfe3e98ac1..9ff2c4a09cdcd 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -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; -- 2.47.3