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Date:   Thu, 15 Dec 2022 13:49:33 +0800
From:   Matt Johnston <matt@...econstruct.com.au>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jeremy Kerr <jk@...econstruct.com.au>,
        alexander.duyck@...il.com
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 https://github.com/openthread/openthread/issues/8523

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 <matt@...econstruct.com.au>
---

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)
 		return;
 
@@ -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))
-- 
2.37.2

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