kni: restrict bifurcated device support

To enable bifurcated device support, rtnl_lock is released before calling
userspace callbacks and asynchronous requests are enabled.

But these changes caused more issues, like bug #809, #816. To reduce the
scope of the problems, the bifurcated device support related changes are
only enabled when it is requested explicitly with new 'enable_bifurcated'
module parameter.
And bifurcated device support is disabled by default.

So the bifurcated device related problems are isolated and they can be
fixed without impacting all use cases.

Bugzilla ID: 816
Fixes: 631217c761 ("kni: fix kernel deadlock with bifurcated device")
Cc: stable@dpdk.org

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Igor Ryzhov <iryzhov@nfware.com>

doc/guides/prog_guide/kernel_nic_interface.rst

@@ -56,6 +56,12 @@ can be specified when the module is loaded to control its behavior:
                     off   Interfaces will be created with carrier state set to off.
                     on    Interfaces will be created with carrier state set to on.
                      (charp)
+    parm:           enable_bifurcated: Enable request processing support for
+                    bifurcated drivers, which means releasing rtnl_lock before calling
+                    userspace callback and supporting async requests (default=off):
+                    on    Enable request processing support for bifurcated drivers.
+                     (charp)
+
 
 Loading the ``rte_kni`` kernel module without any optional parameters is
 the typical way a DPDK application gets packets into and out of the kernel
@@ -174,6 +180,28 @@ To set the default carrier state to *off*:
 If the ``carrier`` parameter is not specified, the default carrier state
 of KNI interfaces will be set to *off*.
 
+.. _kni_bifurcated_device_support:
+
+Bifurcated Device Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+User callbacks are executed while kernel module holds the ``rtnl`` lock, this
+causes a deadlock when callbacks run control commands on another Linux kernel
+network interface.
+
+Bifurcated devices has kernel network driver part and to prevent deadlock for
+them ``enable_bifurcated`` is used.
+
+To enable bifurcated device support:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko enable_bifurcated=on
+
+Enabling bifurcated device support releases ``rtnl`` lock before calling
+callback and locks it back after callback. Also enables asynchronous request to
+support callbacks that requires rtnl lock to work (interface down).
+
 KNI Creation and Deletion
 -------------------------
 

doc/guides/rel_notes/release_21_11.rst

@@ -75,6 +75,12 @@ New Features
     operations.
   * Added multi-process support.
 
+* **Updated default KNI behavior on net devices control callbacks.**
+
+  Updated KNI net devices control callbacks to run with ``rtnl`` kernel lock
+  held by default. A newly added ``enable_bifurcated`` KNI kernel module
+  parameter can be used to run callbacks with ``rtnl`` lock released.
+
 * **Added HiSilicon DMA driver.**
 
   The HiSilicon DMA driver provides device drivers for the Kunpeng's DMA devices.

kernel/linux/kni/kni_dev.h

@@ -34,6 +34,9 @@
 /* Default carrier state for created KNI network interfaces */
 extern uint32_t kni_dflt_carrier;
 
+/* Request processing support for bifurcated drivers. */
+extern uint32_t bifurcated_support;
+
 /**
  * A structure describing the private information for a kni device.
  */

kernel/linux/kni/kni_misc.c

@@ -41,6 +41,10 @@ static uint32_t multiple_kthread_on;
 static char *carrier;
 uint32_t kni_dflt_carrier;
 
+/* Request processing support for bifurcated drivers. */
+static char *enable_bifurcated;
+uint32_t bifurcated_support;
+
 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
 
 static int kni_net_id;
@@ -565,6 +569,22 @@ kni_parse_carrier_state(void)
 	return 0;
 }
 
+static int __init
+kni_parse_bifurcated_support(void)
+{
+	if (!enable_bifurcated) {
+		bifurcated_support = 0;
+		return 0;
+	}
+
+	if (strcmp(enable_bifurcated, "on") == 0)
+		bifurcated_support = 1;
+	else
+		return -1;
+
+	return 0;
+}
+
 static int __init
 kni_init(void)
 {
@@ -590,6 +610,13 @@ kni_init(void)
 	else
 		pr_debug("Default carrier state set to on.\n");
 
+	if (kni_parse_bifurcated_support() < 0) {
+		pr_err("Invalid parameter for bifurcated support\n");
+		return -EINVAL;
+	}
+	if (bifurcated_support == 1)
+		pr_debug("bifurcated support is enabled.\n");
+
 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 	rc = register_pernet_subsys(&kni_net_ops);
 #else
@@ -656,3 +683,12 @@ MODULE_PARM_DESC(carrier,
 "\t\ton    Interfaces will be created with carrier state set to on.\n"
 "\t\t"
 );
+
+module_param(enable_bifurcated, charp, 0644);
+MODULE_PARM_DESC(enable_bifurcated,
+"Enable request processing support for bifurcated drivers, "
+"which means releasing rtnl_lock before calling userspace callback and "
+"supporting async requests (default=off):\n"
+"\t\ton    Enable request processing support for bifurcated drivers.\n"
+"\t\t"
+);

kernel/linux/kni/kni_net.c

@@ -113,12 +113,14 @@ kni_net_process_request(struct net_device *dev, struct rte_kni_request *req)
 
 	ASSERT_RTNL();
 
-	/* If we need to wait and RTNL mutex is held
+	if (bifurcated_support) {
-	 * drop the mutex and hold reference to keep device
+		/* If we need to wait and RTNL mutex is held
-	 */
+		 * drop the mutex and hold reference to keep device
-	if (req->async == 0) {
+		 */
-		dev_hold(dev);
+		if (req->async == 0) {
-		rtnl_unlock();
+			dev_hold(dev);
+			rtnl_unlock();
+		}
 	}
 
 	mutex_lock(&kni->sync_lock);
@@ -132,12 +134,14 @@ kni_net_process_request(struct net_device *dev, struct rte_kni_request *req)
 		goto fail;
 	}
 
-	/* No result available since request is handled
+	if (bifurcated_support) {
-	 * asynchronously. set response to success.
+		/* No result available since request is handled
-	 */
+		 * asynchronously. set response to success.
-	if (req->async != 0) {
+		 */
-		req->result = 0;
+		if (req->async != 0) {
-		goto async;
+			req->result = 0;
+			goto async;
+		}
 	}
 
 	ret_val = wait_event_interruptible_timeout(kni->wq,
@@ -160,9 +164,11 @@ kni_net_process_request(struct net_device *dev, struct rte_kni_request *req)
 
 fail:
 	mutex_unlock(&kni->sync_lock);
-	if (req->async == 0) {
+	if (bifurcated_support) {
-		rtnl_lock();
+		if (req->async == 0) {
-		dev_put(dev);
+			rtnl_lock();
+			dev_put(dev);
+		}
 	}
 	return ret;
 }
@@ -207,8 +213,10 @@ kni_net_release(struct net_device *dev)
 	/* Setting if_up to 0 means down */
 	req.if_up = 0;
 
-	/* request async because of the deadlock problem */
+	if (bifurcated_support) {
-	req.async = 1;
+		/* request async because of the deadlock problem */
+		req.async = 1;
+	}
 
 	ret = kni_net_process_request(dev, &req);