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Date:   Thu, 15 Dec 2022 13:49:33 +0800
From:   Matt Johnston <>
Cc:     "David S. Miller" <>,
        Jakub Kicinski <>,
        Paolo Abeni <>,
        Eric Dumazet <>,
        Jeremy Kerr <>,
Subject: [PATCH net v2] mctp: Remove device type check at unregister

The unregister check could be incorrectly triggered if a netdev
changes its type after register. That is possible for a tun device
using TUNSETLINK ioctl, resulting in mctp unregister failing
and the netdev unregister waiting forever.

This was encountered by

Neither check at register or unregister is required. They were added in
an attempt to track down mctp_ptr being set unexpectedly, which should
not happen in normal operation.

Fixes: 7b1871af75f3 ("mctp: Warn if pointer is set for a wrong dev type")
Signed-off-by: Matt Johnston <>

v2: Also remove the check from register

 net/mctp/device.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/net/mctp/device.c b/net/mctp/device.c
index 99a3bda8852f..acb97b257428 100644
--- a/net/mctp/device.c
+++ b/net/mctp/device.c
@@ -429,12 +429,6 @@ static void mctp_unregister(struct net_device *dev)
 	struct mctp_dev *mdev;
 	mdev = mctp_dev_get_rtnl(dev);
-	if (mdev && !mctp_known(dev)) {
-		// Sanity check, should match what was set in mctp_register
-		netdev_warn(dev, "%s: BUG mctp_ptr set for unknown type %d",
-			    __func__, dev->type);
-		return;
-	}
 	if (!mdev)
@@ -451,14 +445,8 @@ static int mctp_register(struct net_device *dev)
 	struct mctp_dev *mdev;
 	/* Already registered? */
-	mdev = rtnl_dereference(dev->mctp_ptr);
-	if (mdev) {
-		if (!mctp_known(dev))
-			netdev_warn(dev, "%s: BUG mctp_ptr set for unknown type %d",
-				    __func__, dev->type);
+	if (rtnl_dereference(dev->mctp_ptr))
 		return 0;
-	}
 	/* only register specific types */
 	if (!mctp_known(dev))

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