Re: [PATCH net-next 5/7] ibmveth: release the pool kobjects when probe fails

On 10/3/26 7:12 PM, netdev-bot+sashiko@kernel.org wrote:

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- [Medium] On the new err_put_pools path in ibmveth_probe()
   (drivers/net/ethernet/ibm/ibmveth.c), the code calls kobject_put() on…

--

ibmveth: release the pool kobjects when probe fails

This commit adds an err_put_pools unwind label to ibmveth_probe(). The label
calls kobject_put() on each rx_buff_pool[i].kobj before free_netdev(). It is
used when either netif_set_real_num_tx_queues() or register_netdev() fails.

quoted

diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index b89ce389d951f..d5ba2f2650d0f 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c

[ ... ]

quoted

@@ -1981,13 +1980,18 @@ static int ibmveth_probe(struct vio_dev *dev, const struct vio_device_id *id)
  
  	if (rc) {
  		netdev_dbg(netdev, "failed to register netdev rc=%d\n", rc);
-		free_netdev(netdev);
-		return rc;
+		goto err_put_pools;
  	}
  
  	netdev_dbg(netdev, "registered\n");
  
  	return 0;
+
+err_put_pools:
+	for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++)
+		kobject_put(&adapter->rx_buff_pool[i].kobj);
+	free_netdev(netdev);
+	return rc;
  }

[Severity: Medium]
With CONFIG_DEBUG_KOBJECT_RELEASE=y, can this path still free the pool
kobjects while their cleanup is pending?

The kobjects are embedded in netdev_priv(netdev), and ktype_veth_pool has
no release() callback:

static struct kobj_type ktype_veth_pool = {
	.release        = NULL,
	.sysfs_ops      = &veth_pool_ops,
	...
};

On that config, kobject_release() defers the cleanup to a delayed_work
that is embedded in the kobject itself:

lib/kobject.c:kobject_release() {
	...
	INIT_DELAYED_WORK(&kobj->release, kobject_delayed_cleanup);

	schedule_delayed_work(&kobj->release, delay);
	...
}

free_netdev() then frees the adapter while that work is still armed. The
work runs 1 to 4 seconds later. kobject_cleanup() then works on freed
memory: it reads kobj->state_in_sysfs and kobj->name, calls
__kobject_del(), and drops the parent reference.

Until the work runs, the pool%d active, num and size files under
/sys/devices/vio/<unit>/ still exist. A read or write goes through
veth_pool_show() or veth_pool_store(). Both use container_of() to reach
the freed pool, adapter and netdev.

A re-probe in that window could also fail to add pool0. That is the same
failure this commit is meant to fix.

The commit message mentions this and refers to ibmveth_remove(), which
uses the same put-then-free pattern. kobject_cleanup() also reports this
ktype as one that "does not have a release() function, it is broken and
must be fixed".

Calling kobject_del() before kobject_put() would remove the sysfs files
synchronously. However, the delayed_work inside the freed adapter would
still be armed.

Would it make sense to give the pool kobjects their own lifetime? One
option is to allocate them separately with a real release() callback.

Yes. v2 adds a release() for the pool kobjects and waits for it before
free_netdev() in both probe and remove():

|https://lore.kernel.org/netdev/cover.1791178212.git.mmc@linux.ibm.com/| (local)


pw-bot: cr

Thanks,

Mingming