1 files changed, 101 insertions, 10 deletions

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 74f9e4b665e3..3f78c56b58dc 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -511,12 +511,20 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
 
 	dma_fence_enable_sw_signaling(fence);
 
-	trace_dma_fence_wait_start(fence);
+	if (trace_dma_fence_wait_start_enabled()) {
+		rcu_read_lock();
+		trace_dma_fence_wait_start(fence);
+		rcu_read_unlock();
+	}
 	if (fence->ops->wait)
 		ret = fence->ops->wait(fence, intr, timeout);
 	else
 		ret = dma_fence_default_wait(fence, intr, timeout);
-	trace_dma_fence_wait_end(fence);
+	if (trace_dma_fence_wait_end_enabled()) {
+		rcu_read_lock();
+		trace_dma_fence_wait_end(fence);
+		rcu_read_unlock();
+	}
 	return ret;
 }
 EXPORT_SYMBOL(dma_fence_wait_timeout);
@@ -533,16 +541,23 @@ void dma_fence_release(struct kref *kref)
 	struct dma_fence *fence =
 		container_of(kref, struct dma_fence, refcount);
 
+	rcu_read_lock();
 	trace_dma_fence_destroy(fence);
 
-	if (WARN(!list_empty(&fence->cb_list) &&
-		 !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags),
-		 "Fence %s:%s:%llx:%llx released with pending signals!\n",
-		 dma_fence_driver_name(fence),
-		 dma_fence_timeline_name(fence),
-		 fence->context, fence->seqno)) {
+	if (!list_empty(&fence->cb_list) &&
+	    !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
+		const char __rcu *timeline;
+		const char __rcu *driver;
 		unsigned long flags;
 
+		driver = dma_fence_driver_name(fence);
+		timeline = dma_fence_timeline_name(fence);
+
+		WARN(1,
+		     "Fence %s:%s:%llx:%llx released with pending signals!\n",
+		     rcu_dereference(driver), rcu_dereference(timeline),
+		     fence->context, fence->seqno);
+
 		/*
 		 * Failed to signal before release, likely a refcounting issue.
 		 *
@@ -556,6 +571,8 @@ void dma_fence_release(struct kref *kref)
 		spin_unlock_irqrestore(fence->lock, flags);
 	}
 
+	rcu_read_unlock();
+
 	if (fence->ops->release)
 		fence->ops->release(fence);
 	else
@@ -982,11 +999,21 @@ EXPORT_SYMBOL(dma_fence_set_deadline);
  */
 void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq)
 {
+	const char __rcu *timeline;
+	const char __rcu *driver;
+
+	rcu_read_lock();
+
+	timeline = dma_fence_timeline_name(fence);
+	driver = dma_fence_driver_name(fence);
+
 	seq_printf(seq, "%s %s seq %llu %ssignalled\n",
-		   dma_fence_driver_name(fence),
-		   dma_fence_timeline_name(fence),
+		   rcu_dereference(driver),
+		   rcu_dereference(timeline),
 		   fence->seqno,
 		   dma_fence_is_signaled(fence) ? "" : "un");
+
+	rcu_read_unlock();
 }
 EXPORT_SYMBOL(dma_fence_describe);
 
@@ -1055,3 +1082,67 @@ dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops,
 			 BIT(DMA_FENCE_FLAG_SEQNO64_BIT));
 }
 EXPORT_SYMBOL(dma_fence_init64);
+
+/**
+ * dma_fence_driver_name - Access the driver name
+ * @fence: the fence to query
+ *
+ * Returns a driver name backing the dma-fence implementation.
+ *
+ * IMPORTANT CONSIDERATION:
+ * Dma-fence contract stipulates that access to driver provided data (data not
+ * directly embedded into the object itself), such as the &dma_fence.lock and
+ * memory potentially accessed by the &dma_fence.ops functions, is forbidden
+ * after the fence has been signalled. Drivers are allowed to free that data,
+ * and some do.
+ *
+ * To allow safe access drivers are mandated to guarantee a RCU grace period
+ * between signalling the fence and freeing said data.
+ *
+ * As such access to the driver name is only valid inside a RCU locked section.
+ * The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded
+ * by the &rcu_read_lock and &rcu_read_unlock pair.
+ */
+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))
+		return fence->ops->get_driver_name(fence);
+	else
+		return "detached-driver";
+}
+EXPORT_SYMBOL(dma_fence_driver_name);
+
+/**
+ * dma_fence_timeline_name - Access the timeline name
+ * @fence: the fence to query
+ *
+ * Returns a timeline name provided by the dma-fence implementation.
+ *
+ * IMPORTANT CONSIDERATION:
+ * Dma-fence contract stipulates that access to driver provided data (data not
+ * directly embedded into the object itself), such as the &dma_fence.lock and
+ * memory potentially accessed by the &dma_fence.ops functions, is forbidden
+ * after the fence has been signalled. Drivers are allowed to free that data,
+ * and some do.
+ *
+ * To allow safe access drivers are mandated to guarantee a RCU grace period
+ * between signalling the fence and freeing said data.
+ *
+ * As such access to the driver name is only valid inside a RCU locked section.
+ * The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded
+ * by the &rcu_read_lock and &rcu_read_unlock pair.
+ */
+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))
+		return fence->ops->get_driver_name(fence);
+	else
+		return "signaled-timeline";
+}
+EXPORT_SYMBOL(dma_fence_timeline_name);