[PATCH v3 03/14] iommu/ioasid: Add a separate function for detach data

[Jacob Pan <jacob.pan.linux@xxxxxxxxx>]

IOASID private data can be cleared by ioasid_attach_data() with a NULL
data pointer. A common use case is for a caller to free the data
afterward. ioasid_attach_data() calls synchronize_rcu() before return
such that free data can be sure without outstanding readers.
However, since synchronize_rcu() may sleep, ioasid_attach_data() cannot
be used under spinlocks.

This patch adds ioasid_detach_data() as a separate API where
synchronize_rcu() is called only in this case. ioasid_attach_data() can
then be used under spinlocks. In addition, this change makes the API
symmetrical.

Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
 drivers/iommu/intel/svm.c |  4 ++--
 drivers/iommu/ioasid.c    | 54 ++++++++++++++++++++++++++++++++++++++---------
 include/linux/ioasid.h    |  5 ++++-
 3 files changed, 50 insertions(+), 13 deletions(-)

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 2c5645f0737a..06a16bee7b65 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -398,7 +398,7 @@ int intel_svm_bind_gpasid(struct iommu_domain *domain, struct device *dev,
 	list_add_rcu(&sdev->list, &svm->devs);
  out:
 	if (!IS_ERR_OR_NULL(svm) && list_empty(&svm->devs)) {
-		ioasid_attach_data(data->hpasid, NULL);
+		ioasid_detach_data(data->hpasid);
 		kfree(svm);
 	}
 
@@ -441,7 +441,7 @@ int intel_svm_unbind_gpasid(struct device *dev, int pasid)
 				 * the unbind, IOMMU driver will get notified
 				 * and perform cleanup.
 				 */
-				ioasid_attach_data(pasid, NULL);
+				ioasid_detach_data(pasid);
 				kfree(svm);
 			}
 		}
diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
index 5f63af07acd5..6cfbdfb492e0 100644
--- a/drivers/iommu/ioasid.c
+++ b/drivers/iommu/ioasid.c
@@ -272,24 +272,58 @@ int ioasid_attach_data(ioasid_t ioasid, void *data)
 
 	spin_lock(&ioasid_allocator_lock);
 	ioasid_data = xa_load(&active_allocator->xa, ioasid);
-	if (ioasid_data)
-		rcu_assign_pointer(ioasid_data->private, data);
-	else
+
+	if (!ioasid_data) {
 		ret = -ENOENT;
-	spin_unlock(&ioasid_allocator_lock);
+		goto done_unlock;
+	}
 
-	/*
-	 * Wait for readers to stop accessing the old private data, so the
-	 * caller can free it.
-	 */
-	if (!ret)
-		synchronize_rcu();
+	if (ioasid_data->private) {
+		ret = -EBUSY;
+		goto done_unlock;
+	}
+	rcu_assign_pointer(ioasid_data->private, data);
+
+done_unlock:
+	spin_unlock(&ioasid_allocator_lock);
 
 	return ret;
 }
 EXPORT_SYMBOL_GPL(ioasid_attach_data);
 
 /**
+ * ioasid_detach_data - Clear the private data of an ioasid
+ *
+ * @ioasid: the IOASIDD to clear private data
+ */
+void ioasid_detach_data(ioasid_t ioasid)
+{
+	struct ioasid_data *ioasid_data;
+
+	spin_lock(&ioasid_allocator_lock);
+	ioasid_data = xa_load(&active_allocator->xa, ioasid);
+
+	if (!ioasid_data) {
+		pr_warn("IOASID %u not found to detach data from\n", ioasid);
+		goto done_unlock;
+	}
+
+	if (ioasid_data->private) {
+		rcu_assign_pointer(ioasid_data->private, NULL);
+		goto done_unlock;
+	}
+
+done_unlock:
+	spin_unlock(&ioasid_allocator_lock);
+	/*
+	 * Wait for readers to stop accessing the old private data,
+	 * so the caller can free it.
+	 */
+	synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(ioasid_detach_data);
+
+/**
  * ioasid_alloc - Allocate an IOASID
  * @set: the IOASID set
  * @min: the minimum ID (inclusive)
diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
index 9c44947a68c8..c7f649fa970a 100644
--- a/include/linux/ioasid.h
+++ b/include/linux/ioasid.h
@@ -40,7 +40,7 @@ void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
 void ioasid_unregister_allocator(struct ioasid_allocator_ops *allocator);
 int ioasid_attach_data(ioasid_t ioasid, void *data);
-
+void ioasid_detach_data(ioasid_t ioasid);
 #else /* !CONFIG_IOASID */
 static inline ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
 				    ioasid_t max, void *private)
@@ -72,5 +72,8 @@ static inline int ioasid_attach_data(ioasid_t ioasid, void *data)
 	return -ENOTSUPP;
 }
 
+static inline void ioasid_detach_data(ioasid_t ioasid)
+{
+}
 #endif /* CONFIG_IOASID */
 #endif /* __LINUX_IOASID_H */
-- 
2.7.4