Re: [PATCH net] net: dsa: remove redundant netdev_lock_ops() from conduit ethtool ops

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi Stanislav,

On 15/04/2026 01:10, Stanislav Fomichev wrote:
> DSA replaces the conduit (master) device's ethtool_ops with its own
> wrappers that aggregate stats from both the conduit and DSA switch
> ports. Taking the lock again inside the DSA wrappers causes a deadlock.
> 
> Stumbled upon this when booting qemu with fbnic and CONFIG_NET_DSA_LOOP=y
> (which looks like some kind of testing device that auto-populates the ports
> of eth0). `ethtool -i` is enough to deadlock. This means we have basically zero
> coverage for DSA stuff with real ops locked devs.

True, indeed I don't have physical devices here with locked ops, looking
at the current devices that use it (fbnic, bnxt, gve, mlx5, bnge) that's
not too surprising, I don't think these are often used with DSA.

> 
> Remove the redundant netdev_lock_ops()/netdev_unlock_ops() calls from
> the DSA conduit ethtool wrappers.
> 
> Cc: Maxime Chevallier <maxime.chevallier@bootlin.com>
> Fixes: 2bcf4772e45a ("net: ethtool: try to protect all callback with netdev instance lock")
> Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
> (cherry picked from commit 1538c00ab3212273240112bd53692d54d95f2dd5)

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime
> ---
>  net/dsa/conduit.c | 16 +---------------
>  1 file changed, 1 insertion(+), 15 deletions(-)
> 
> diff --git a/net/dsa/conduit.c b/net/dsa/conduit.c
> index a1b044467bd6..8398d72d7e4d 100644
> --- a/net/dsa/conduit.c
> +++ b/net/dsa/conduit.c
> @@ -27,9 +27,7 @@ static int dsa_conduit_get_regs_len(struct net_device *dev)
>  	int len;
>  
>  	if (ops && ops->get_regs_len) {
> -		netdev_lock_ops(dev);
>  		len = ops->get_regs_len(dev);
> -		netdev_unlock_ops(dev);
>  		if (len < 0)
>  			return len;
>  		ret += len;
> @@ -60,15 +58,11 @@ static void dsa_conduit_get_regs(struct net_device *dev,
>  	int len;
>  
>  	if (ops && ops->get_regs_len && ops->get_regs) {
> -		netdev_lock_ops(dev);
>  		len = ops->get_regs_len(dev);
> -		if (len < 0) {
> -			netdev_unlock_ops(dev);
> +		if (len < 0)
>  			return;
> -		}
>  		regs->len = len;
>  		ops->get_regs(dev, regs, data);
> -		netdev_unlock_ops(dev);
>  		data += regs->len;
>  	}
>  
> @@ -115,10 +109,8 @@ static void dsa_conduit_get_ethtool_stats(struct net_device *dev,
>  	int count, mcount = 0;
>  
>  	if (ops && ops->get_sset_count && ops->get_ethtool_stats) {
> -		netdev_lock_ops(dev);
>  		mcount = ops->get_sset_count(dev, ETH_SS_STATS);
>  		ops->get_ethtool_stats(dev, stats, data);
> -		netdev_unlock_ops(dev);
>  	}
>  
>  	list_for_each_entry(dp, &dst->ports, list) {
> @@ -149,10 +141,8 @@ static void dsa_conduit_get_ethtool_phy_stats(struct net_device *dev,
>  		if (count >= 0)
>  			phy_ethtool_get_stats(dev->phydev, stats, data);
>  	} else if (ops && ops->get_sset_count && ops->get_ethtool_phy_stats) {
> -		netdev_lock_ops(dev);
>  		count = ops->get_sset_count(dev, ETH_SS_PHY_STATS);
>  		ops->get_ethtool_phy_stats(dev, stats, data);
> -		netdev_unlock_ops(dev);
>  	}
>  
>  	if (count < 0)
> @@ -176,13 +166,11 @@ static int dsa_conduit_get_sset_count(struct net_device *dev, int sset)
>  	struct dsa_switch_tree *dst = cpu_dp->dst;
>  	int count = 0;
>  
> -	netdev_lock_ops(dev);
>  	if (sset == ETH_SS_PHY_STATS && dev->phydev &&
>  	    (!ops || !ops->get_ethtool_phy_stats))
>  		count = phy_ethtool_get_sset_count(dev->phydev);
>  	else if (ops && ops->get_sset_count)
>  		count = ops->get_sset_count(dev, sset);
> -	netdev_unlock_ops(dev);
>  
>  	if (count < 0)
>  		count = 0;
> @@ -239,7 +227,6 @@ static void dsa_conduit_get_strings(struct net_device *dev, u32 stringset,
>  	struct dsa_switch_tree *dst = cpu_dp->dst;
>  	int count, mcount = 0;
>  
> -	netdev_lock_ops(dev);
>  	if (stringset == ETH_SS_PHY_STATS && dev->phydev &&
>  	    !ops->get_ethtool_phy_stats) {
>  		mcount = phy_ethtool_get_sset_count(dev->phydev);
> @@ -253,7 +240,6 @@ static void dsa_conduit_get_strings(struct net_device *dev, u32 stringset,
>  			mcount = 0;
>  		ops->get_strings(dev, stringset, data);
>  	}
> -	netdev_unlock_ops(dev);
>  
>  	list_for_each_entry(dp, &dst->ports, list) {
>  		if (!dsa_port_is_dsa(dp) && !dsa_port_is_cpu(dp))