Patch "i40evf: don't rely on netif_running() outside rtnl_lock()" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

i40evf: don't rely on netif_running() outside rtnl_lock()

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
i40evf-don-t-rely-on-netif_running-outside-rtnl_lock.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jacob Keller <[email protected]>
Date: Fri, 27 Oct 2017 11:06:49 -0400
Subject: i40evf: don't rely on netif_running() outside rtnl_lock()

From: Jacob Keller <[email protected]>

[ Upstream commit 44b034b406211fc103159f82b9e601e05675c739 ]

In i40evf_reset_task we use netif_running() to determine whether or not the device is currently up. This allows us to properly free queue memory and shut down things before we request the hardware reset.

It turns out that we cannot be guaranteed of netif_running() returning false until the device is fully up, as the kernel core code sets __LINK_STATE_START prior to calling .ndo_open. Since we're not holding the rtnl_lock(), it's possible that the driver's i40evf_open handler function is currently being called while we're resetting.

We can't simply hold the rtnl_lock() while checking netif_running() as this could cause a deadlock with the i40evf_open() function. Additionally, we can't avoid the deadlock by holding the rtnl_lock() over the whole reset path, as this essentially serializes all resets, and can cause massive delays if we have multiple VFs on a system.

Instead, lets just check our own internal state __I40EVF_RUNNING state field. This allows us to ensure that the state is correct and is only set after we've finished bringing the device up.

Without this change we might free data structures about device queues and other memory before they've been fully allocated.

---
 drivers/net/ethernet/intel/i40evf/i40evf_main.c |   20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

@@ -1775,7 +1775,11 @@ static void i40evf_disable_vf(struct i40
 
 	adapter->flags |= I40EVF_FLAG_PF_COMMS_FAILED;
 
-	if (netif_running(adapter->netdev)) {
+	/* We don't use netif_running() because it may be true prior to
+	 * ndo_open() returning, so we can't assume it means all our open
+	 * tasks have finished, since we're not holding the rtnl_lock here.
+	 */
+	if (adapter->state == __I40EVF_RUNNING) {
 		set_bit(__I40E_VSI_DOWN, adapter->vsi.state);
 		netif_carrier_off(adapter->netdev);
 		netif_tx_disable(adapter->netdev);

@@ -1833,6 +1837,7 @@ static void i40evf_reset_task(struct wor
 	struct i40evf_mac_filter *f;
 	u32 reg_val;
 	int i = 0, err;
+	bool running;
 
 	while (test_and_set_bit(__I40EVF_IN_CLIENT_TASK,
 				&adapter->crit_section))

@@ -1892,7 +1897,13 @@ static void i40evf_reset_task(struct wor
 	}
 
 continue_reset:
-	if (netif_running(netdev)) {
+	/* We don't use netif_running() because it may be true prior to
+	 * ndo_open() returning, so we can't assume it means all our open
+	 * tasks have finished, since we're not holding the rtnl_lock here.
+	 */
+	running = (adapter->state == __I40EVF_RUNNING);
+
+	if (running) {
 		netif_carrier_off(netdev);
 		netif_tx_stop_all_queues(netdev);
 		adapter->link_up = false;

@@ -1936,7 +1947,10 @@ continue_reset:
 
 	mod_timer(&adapter->watchdog_timer, jiffies + 2);
 
-	if (netif_running(adapter->netdev)) {
+	/* We were running when the reset started, so we need to restore some
+	 * state here.
+	 */
+	if (running) {
 		/* allocate transmit descriptors */
 		err = i40evf_setup_all_tx_resources(adapter);
 		if (err)

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/i40evf-don-t-rely-on-netif_running-outside-rtnl_lock.patch