net: mctp: tests: create test skbs with the correct net and device

In our test skb creation functions, we're not setting up the net and
device data. This doesn't matter at the moment, but we will want to add
support for distinct net IDs in future.

Set the ->net identifier on the test MCTP device, and ensure that test
skbs are set up with the correct device-related data on creation. Create
a helper for setting skb->dev and mctp_skb_cb->net.

We have a few cases where we're calling __mctp_cb() to initialise the cb
(which we need for the above) separately, so integrate this into the skb
creation helpers.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

mctp: make __mctp_dev_get() take a refcount hold

Previously there was a race that could allow the mctp_dev refcount
to hit zero:

rcu_read_lock();
mdev = __mctp_dev_get(dev);
// mctp_unregister() happens here, mdev->refs hits zero
mctp_dev_hold(dev);
rcu_read_unlock();

Now we make __mctp_dev_get() take the hold itself. It is safe to test
against the zero refcount because __mctp_dev_get() is called holding
rcu_read_lock and mctp_dev uses kfree_rcu().

Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

mctp: test: fix skb free in test device tx

In our test device, we're currently freeing skbs in the transmit path
with kfree(), rather than kfree_skb(). This change uses the correct
kfree_skb() instead.

Fixes: ded21b722995 ("mctp: Add test utils")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

mctp: Add test utils

Add a new object for shared test utilities

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

Revert "Merge branch 'mctp-kunit-tests'"

This reverts commit 4f42ad2011d2fcbd89f5cdf56121271a8cd5ee5d, reversing
changes made to ea2dd331bfaaeba74ba31facf437c29044f7d4cb.

These chanfges break the build when mctp is modular.

Signed-off-by: David S. Miller <davem@davemloft.net>

mctp: Add test utils

Add a new object for shared test utilities

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>