netdev - [PATCH net-next 2/2] net-sysfs: warn if new queue objects are being created during device unregistration

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Date:   Tue,  7 Dec 2021 15:57:25 +0100
From:   Antoine Tenart <atenart@...nel.org>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     Antoine Tenart <atenart@...nel.org>, alexander.duyck@...il.com,
        netdev@...r.kernel.org
Subject: [PATCH net-next 2/2] net-sysfs: warn if new queue objects are being created during device unregistration

Calling netdev_queue_update_kobjects is allowed during device
unregistration since commit 5c56580b74e5 ("net: Adjust TX queue kobjects
if number of queues changes during unregister"). But this is solely to
allow queue unregistrations. Any path attempting to add new queues after
a device started its unregistration should be fixed.

This patch adds a warning to detect such illegal use.

Signed-off-by: Antoine Tenart <atenart@...nel.org>
---
 net/core/net-sysfs.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 33f408c24205..53ea262ecafd 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1694,6 +1694,13 @@ netdev_queue_update_kobjects(struct net_device *dev, int old_num, int new_num)
 	int i;
 	int error = 0;
 
+	/* Tx queue kobjects are allowed to be updated when a device is being
+	 * unregistered, but solely to remove queues from qdiscs. Any path
+	 * adding queues should be fixed.
+	 */
+	WARN(dev->reg_state == NETREG_UNREGISTERING && new_num > old_num,
+	     "New queues can't be registered after device unregistration.");
+
 	for (i = old_num; i < new_num; i++) {
 		error = netdev_queue_add_kobject(dev, i);
 		if (error) {
-- 
2.33.1