netdev - Re: [PATCH net] net: Lock lower level devices when updating features

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Message-ID: <aBpJi3t0RhUj5HPE@mini-arch>
Date: Tue, 6 May 2025 10:40:27 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Cosmin Ratiu <cratiu@...dia.com>
Cc: netdev@...r.kernel.org, Stanislav Fomichev <sdf@...ichev.me>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"jiri @ resnulli . us" <jiri@...nulli.us>,
	Saeed Mahameed <saeedm@...dia.com>,
	Dragos Tatulea <dtatulea@...dia.com>,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net] net: Lock lower level devices when updating features

On 05/06, Stanislav Fomichev wrote:
> On 05/06, Cosmin Ratiu wrote:
> > __netdev_update_features() expects the netdevice to be ops-locked, but
> > it gets called recursively on the lower level netdevices to sync their
> > features, and nothing locks those.
> > 
> > This commit fixes that, with the assumption that it shouldn't be possible
> > for both higher-level and lover-level netdevices to require the instance
> > lock, because that would lead to lock dependency warnings.
> > 
> > Without this, playing with higher level (e.g. vxlan) netdevices on top
> > of netdevices with instance locking enabled can run into issues:
> 
> Mentioning vxlan is a bit confusing here; it shouldn't let you flip lro (I
> think). Which upper are you testing against?
> 
> Trying to understand if we can cover this case in the selftests.
> netdevsim also doesn't expose F_LRO feature... (yet?)

Ok, yeah, I can see it with the teaming on top of netdevsim and the following
patch applied. Might try to send a testcase to cover this and the promisc part
that I missed.

Acked-by: Stanislav Fomichev <sdf@...ichev.me>

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 2aa999345fe1..af545d42961c 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -881,11 +881,13 @@ static void nsim_setup(struct net_device *dev)
 			 NETIF_F_SG |
 			 NETIF_F_FRAGLIST |
 			 NETIF_F_HW_CSUM |
+			 NETIF_F_LRO |
 			 NETIF_F_TSO;
 	dev->hw_features |= NETIF_F_HW_TC |
 			    NETIF_F_SG |
 			    NETIF_F_FRAGLIST |
 			    NETIF_F_HW_CSUM |
+			    NETIF_F_LRO |
 			    NETIF_F_TSO;
 	dev->max_mtu = ETH_MAX_MTU;
 	dev->xdp_features = NETDEV_XDP_ACT_HW_OFFLOAD;