qcacld-3.0: Reject down the tree transitions instead of waiting

The driver currently waits for driver transitions (loading/unloading)
to complete before allowing a psoc or vdev level transition/operation.
This can lead to race conditions if the driver acquires rtnl lock as a part
of the operation and simultaneously a driver transition is invoked.

One such scenario occurs if delete virtual interface is invoked in parallel
to rmmod. The timing of the calls can be such that the delete interface is
waiting on DSC queue to complete after rmmod while the rmmod is waiting on
the rtnl lock to be freed by the delete interface resulting in a scenario
where the threads are waiting on the other to complete.

* Thread B - Invokes rmmod and context switch happens before rtnl lock is
             taken

* Thread A - Takes rtnl lock and invokes iw dev wlan0 del
	   - Context switch after entering wlan_hdd_del_virtual_intf
	     before osif_vdev_sync_trans_start_wait

* Thread B - Waits for rtnl lock to be released by Thread A

* Thread A - Waits for driver transition to be completed by Thread B

To avoid this possible scenario, modify the infrastructure such that any
down the tree transitions/operations are rejected if a driver transition
is taking place instead of waiting. Also, modify the corresponding tests
in the DSC unit test framework to correctly verify the changes made.

Change-Id: I61715c8fc2df33fd2deb46389da0375e4df5080c
CRs-Fixed: 2475386

components/dsc/src/wlan_dsc_psoc.c

@@ -126,11 +126,34 @@ static bool __dsc_psoc_trans_active_down_tree(struct dsc_psoc *psoc)
 
 #define __dsc_psoc_can_op(psoc) __dsc_psoc_can_trans(psoc)
 
-static bool __dsc_psoc_can_trans(struct dsc_psoc *psoc)
+/*
+ * __dsc_psoc_can_trans() - Returns if the psoc transition can occur or not
+ * @psoc: The DSC psoc
+ *
+ * This function checks if the psoc transition can occur or not by checking if
+ * any other down the tree/up the tree transition/operation is taking place.
+ *
+ * If there are any driver transition taking place, then the psoc trans/ops
+ * should be rejected and not queued in the DSC queue. Return QDF_STATUS_E_INVAL
+ * in this case.
+ *
+ * If there any psoc or vdev trans/ops is taking place, then the psoc trans/ops
+ * should be rejected and queued in the DSC queue so that it may be resumed
+ * after the current trans/ops is completed. Return QDF_STATUS_E_AGAIN in this
+ * case.
+ *
+ * Return: QDF_STATUS_SUCCESS if transition is allowed, error code if not.
+ */
+static QDF_STATUS __dsc_psoc_can_trans(struct dsc_psoc *psoc)
 {
-	return !__dsc_trans_active_or_queued(&psoc->driver->trans) &&
-		!__dsc_trans_active_or_queued(&psoc->trans) &&
-		!__dsc_psoc_trans_active_down_tree(psoc);
+	if (__dsc_trans_active_or_queued(&psoc->driver->trans))
+		return QDF_STATUS_E_INVAL;
+
+	if (__dsc_trans_active_or_queued(&psoc->trans) ||
+	    __dsc_psoc_trans_active_down_tree(psoc))
+		return QDF_STATUS_E_AGAIN;
+
+	return QDF_STATUS_SUCCESS;
 }
 
 static bool __dsc_psoc_can_trigger(struct dsc_psoc *psoc)
@@ -143,8 +166,11 @@ static bool __dsc_psoc_can_trigger(struct dsc_psoc *psoc)
 static QDF_STATUS
 __dsc_psoc_trans_start_nolock(struct dsc_psoc *psoc, const char *desc)
 {
-	if (!__dsc_psoc_can_trans(psoc))
-		return QDF_STATUS_E_AGAIN;
+	QDF_STATUS status;
+
+	status = __dsc_psoc_can_trans(psoc);
+	if (QDF_IS_STATUS_ERROR(status))
+		return status;
 
 	return __dsc_trans_start(&psoc->trans, desc);
 }
@@ -194,7 +220,7 @@ __dsc_psoc_trans_start_wait(struct dsc_psoc *psoc, const char *desc)
 
 	/* try to start without waiting */
 	status = __dsc_psoc_trans_start_nolock(psoc, desc);
-	if (QDF_IS_STATUS_SUCCESS(status))
+	if (QDF_IS_STATUS_SUCCESS(status) || status == QDF_STATUS_E_INVAL)
 		goto unlock;
 
 	status = __dsc_trans_queue(&psoc->trans, &tran, desc);
@@ -298,10 +324,9 @@ static QDF_STATUS __dsc_psoc_op_start(struct dsc_psoc *psoc, const char *func)
 
 	__dsc_driver_lock(psoc);
 
-	if (!__dsc_psoc_can_op(psoc)) {
-		status = QDF_STATUS_E_AGAIN;
+	status = __dsc_psoc_can_op(psoc);
+	if (QDF_IS_STATUS_ERROR(status))
 		goto unlock;
-	}
 
 	status = __dsc_ops_insert(&psoc->ops, func);
 
@@ -349,9 +374,6 @@ static void __dsc_psoc_wait_for_ops(struct dsc_psoc *psoc)
 
 	__dsc_driver_lock(psoc);
 
-	/* flushing without preventing new ops is almost certainly a bug */
-	dsc_assert(!__dsc_psoc_can_op(psoc));
-
 	wait = psoc->ops.count > 0;
 	if (wait)
 		qdf_event_reset(&psoc->ops.event);

components/dsc/src/wlan_dsc_vdev.c

@@ -108,18 +108,44 @@ void dsc_vdev_destroy(struct dsc_vdev **out_vdev)
 
 #define __dsc_vdev_can_op(vdev) __dsc_vdev_can_trans(vdev)
 
-static bool __dsc_vdev_can_trans(struct dsc_vdev *vdev)
+/*
+ * __dsc_vdev_can_trans() - Returns if the vdev transition can occur or not
+ * @vdev: The DSC vdev
+ *
+ * This function checks if the vdev transition can occur or not by checking if
+ * any other down the tree/up the tree transition/operation is taking place.
+ *
+ * If there are any driver transition taking place, then the vdev trans/ops
+ * should be rejected and not queued in the DSC queue. Return QDF_STATUS_E_INVAL
+ * in this case.
+ *
+ * If there any psoc or vdev trans/ops is taking place, then the vdev trans/ops
+ * should be rejected and queued in the DSC queue so that it may be resumed
+ * after the current trans/ops is completed. Return QDF_STATUS_E_AGAIN in this
+ * case.
+ *
+ * Return: QDF_STATUS_SUCCESS if transition is allowed, error code if not.
+ */
+static QDF_STATUS __dsc_vdev_can_trans(struct dsc_vdev *vdev)
 {
-	return !__dsc_trans_active_or_queued(&vdev->psoc->driver->trans) &&
-		!__dsc_trans_active_or_queued(&vdev->psoc->trans) &&
-		!__dsc_trans_active_or_queued(&vdev->trans);
+	if (__dsc_trans_active_or_queued(&vdev->psoc->driver->trans))
+		return QDF_STATUS_E_INVAL;
+
+	if (__dsc_trans_active_or_queued(&vdev->psoc->trans) ||
+	    __dsc_trans_active_or_queued(&vdev->trans))
+		return QDF_STATUS_E_AGAIN;
+
+	return QDF_STATUS_SUCCESS;
 }
 
 static QDF_STATUS
 __dsc_vdev_trans_start_nolock(struct dsc_vdev *vdev, const char *desc)
 {
-	if (!__dsc_vdev_can_trans(vdev))
-		return QDF_STATUS_E_AGAIN;
+	QDF_STATUS status = QDF_STATUS_SUCCESS;
+
+	status = __dsc_vdev_can_trans(vdev);
+	if (QDF_IS_STATUS_ERROR(status))
+		return status;
 
 	return __dsc_trans_start(&vdev->trans, desc);
 }
@@ -169,7 +195,7 @@ __dsc_vdev_trans_start_wait(struct dsc_vdev *vdev, const char *desc)
 
 	/* try to start without waiting */
 	status = __dsc_vdev_trans_start_nolock(vdev, desc);
-	if (QDF_IS_STATUS_SUCCESS(status))
+	if (QDF_IS_STATUS_SUCCESS(status) || status == QDF_STATUS_E_INVAL)
 		goto unlock;
 
 	status = __dsc_trans_queue(&vdev->trans, &tran, desc);
@@ -259,10 +285,9 @@ static QDF_STATUS __dsc_vdev_op_start(struct dsc_vdev *vdev, const char *func)
 
 	__dsc_driver_lock(vdev);
 
-	if (!__dsc_vdev_can_op(vdev)) {
-		status = QDF_STATUS_E_AGAIN;
+	status = __dsc_vdev_can_op(vdev);
+	if (QDF_IS_STATUS_ERROR(status))
 		goto unlock;
-	}
 
 	status = __dsc_ops_insert(&vdev->ops, func);
 
@@ -316,9 +341,6 @@ static void __dsc_vdev_wait_for_ops(struct dsc_vdev *vdev)
 
 	__dsc_driver_lock(vdev);
 
-	/* flushing without preventing new ops is almost certainly a bug */
-	dsc_assert(!__dsc_vdev_can_op(vdev));
-
 	wait = vdev->ops.count > 0;
 	if (wait)
 		qdf_event_reset(&vdev->ops.event);

components/dsc/test/wlan_dsc_test.c

@@ -200,7 +200,6 @@ static uint32_t dsc_test_driver_trans_blocks(void)
 	}
 
 	/* test */
-
 	/* a driver in transition should cause ... */
 	action_expect(driver, trans, QDF_STATUS_SUCCESS, errors);
 
@@ -210,13 +209,13 @@ static uint32_t dsc_test_driver_trans_blocks(void)
 
 	/* ... children psoc trans/ops to fail */
 	dsc_for_each_driver_psoc(driver, psoc) {
-		action_expect(psoc, trans, QDF_STATUS_E_AGAIN, errors);
-		action_expect(psoc, op, QDF_STATUS_E_AGAIN, errors);
+		action_expect(psoc, trans, QDF_STATUS_E_INVAL, errors);
+		action_expect(psoc, op, QDF_STATUS_E_INVAL, errors);
 
 		/* ... grandchildren vdev trans/ops to fail */
 		dsc_for_each_psoc_vdev(psoc, vdev) {
-			action_expect(vdev, trans, QDF_STATUS_E_AGAIN, errors);
-			action_expect(vdev, op, QDF_STATUS_E_AGAIN, errors);
+			action_expect(vdev, trans, QDF_STATUS_E_INVAL, errors);
+			action_expect(vdev, op, QDF_STATUS_E_INVAL, errors);
 		}
 	}
 
@@ -251,7 +250,6 @@ static uint32_t dsc_test_psoc_trans_blocks(void)
 	}
 
 	/* test */
-
 	/* a psoc in transition should cause ... */
 	psoc = nth_psoc(driver, 1);
 	action_expect(psoc, trans, QDF_STATUS_SUCCESS, errors);