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

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Message-ID: <aBpC9_SgUaAA2P0f@mini-arch>
Date: Tue, 6 May 2025 10:12:23 -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, 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?)