Re: [net PATCH v2 1/6] net: ethtool: keep rtnl_lock for the ioctl self test

[Simon Horman <horms@kernel.org>]

On Mon, Sep 14, 2026 at 02:09:57PM -0700, Alexander Duyck wrote:
> From: Alexander Duyck <alexanderduyck@fb.com>
> 
> An offline self test that brings the interface down and back up with
> netif_close() / netif_open() requires rtnl_lock for both. Since the
> ethtool IOCTL path became rtnl-optional for ops-locked drivers, the
> ETHTOOL_TEST ioctl runs holding only the netdev instance lock, so on an
> ops-locked driver the self test now tears the device down without
> rtnl_lock.
> 
> With lockdep this reproduces deterministically on every offline self
> test on such a driver; note the sole lock held is the instance lock, not
> rtnl:
> 
>   WARNING: suspicious RCU usage
>   net/core/netpoll.c:207 suspicious rcu_dereference_protected() usage!
>   1 lock held by ethtool/107:
>    #0: (&dev->lock){+.+.}, at: dev_ethtool
>   Call Trace:
>    netpoll_poll_disable
>    __dev_close_many
>    netif_close_many
>    netif_close
>    fbnic_self_test
>    dev_ethtool_locked
>    dev_ethtool
>    dev_ioctl
>    sock_ioctl
>    __x64_sys_ioctl
> 
> Without lockdep the same condition trips ASSERT_RTNL() in
> __dev_close_many() / __dev_open(); that check only samples the global
> rtnl state, so it can be masked by a concurrent rtnl holder, but the
> device is still being reconfigured without the lock it requires.
> 
> The ethtool self_test is a legacy ioctl-only command, so an ETHTOOL_TEST
> case is only needed on the ioctl path. Add an opt-in bit for drivers whose
> self test needs rtnl_lock and set it on the ops-locked drivers whose
> offline self test tears the interface down and up:
> 
>   - fbnic (ops-locked via queue_mgmt_ops): fbnic_self_test() offline path
>     uses netif_close() / netif_open().
>   - bnxt (ops-locked via queue_mgmt_ops): bnxt_self_test() offline path
>     goes through bnxt_close_nic() / bnxt_half_open_nic() /
>     bnxt_half_close_nic() / bnxt_open_nic(), which close and reopen the
>     device.
> 
> Fixes: f994752b1127 ("net: ethtool: optionally skip rtnl_lock on IOCTL path")
> Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>

Reviewed-by: Simon Horman <horms@kernel.org>