Re: [RFC net-next 1/4] net: Hold netdev instance lock during ndo_open/ndo_stop

[Joe Damato <jdamato@fastly.com>]

On Tue, Feb 04, 2025 at 03:00:54PM -0800, Stanislav Fomichev wrote:
> For the drivers that use shaper API, switch to the mode where
> core stack holds the netdev lock. This affects two drivers:
> 
> * iavf - already grabs netdev lock in ndo_open/ndo_stop, so mostly
>          remove these
> * netdevsim - switch to _locked APIs to avoid deadlock
> 
> Cc: Saeed Mahameed <saeed@kernel.org>
> Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
> ---
>  Documentation/networking/netdevices.rst     |  6 ++++--
>  drivers/net/ethernet/intel/iavf/iavf_main.c | 14 ++++++-------
>  drivers/net/netdevsim/netdev.c              | 14 ++++++++-----
>  include/linux/netdevice.h                   | 23 +++++++++++++++++++++
>  net/core/dev.c                              | 12 +++++++++++
>  net/core/dev.h                              |  6 ++++--
>  6 files changed, 58 insertions(+), 17 deletions(-)

[...]

> @@ -4474,12 +4471,12 @@ static int iavf_close(struct net_device *netdev)
>  	u64 aq_to_restore;
>  	int status;
>  
> -	netdev_lock(netdev);
> +	netdev_assert_locked(netdev);
> +
>  	mutex_lock(&adapter->crit_lock);
>  
>  	if (adapter->state <= __IAVF_DOWN_PENDING) {
>  		mutex_unlock(&adapter->crit_lock);
> -		netdev_unlock(netdev);
>  		return 0;
>  	}
>  
> @@ -4532,6 +4529,7 @@ static int iavf_close(struct net_device *netdev)
>  	if (!status)
>  		netdev_warn(netdev, "Device resources not yet released\n");
>  
> +	netdev_lock(netdev);

I'm probably just misreading the rest of the patch, but I was just
wondering: is this netdev_lock call here intentional? I am asking
because I thought the lock was taken in ndo_stop before this is
called?