netdev - Re: [PATCH net-next v2 04/11] net: add netdev->up protected by netdev

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Message-ID: <20250115084553.38636-1-kuniyu@amazon.com>
Date: Wed, 15 Jan 2025 17:45:53 +0900
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <kuba@...nel.org>
CC: <andrew+netdev@...n.ch>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<horms@...nel.org>, <jdamato@...tly.com>, <netdev@...r.kernel.org>,
	<pabeni@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>
Subject: Re: [PATCH net-next v2 04/11] net: add netdev->up protected by netdev_lock()

From: Jakub Kicinski <kuba@...nel.org>
Date: Tue, 14 Jan 2025 19:53:12 -0800
> Some uAPI (netdev netlink) hide net_device's sub-objects while
> the interface is down to ensure uniform behavior across drivers.
> To remove the rtnl_lock dependency from those uAPIs we need a way
> to safely tell if the device is down or up.
> 
> Add an indication of whether device is open or closed, protected
> by netdev->lock. The semantics are the same as IFF_UP, but taking
> netdev_lock around every write to ->flags would be a lot of code
> churn.
> 
> We don't want to blanket the entire open / close path by netdev_lock,
> because it will prevent us from applying it to specific structures -
> core helpers won't be able to take that lock from any function
> called by the drivers on open/close paths.
> 
> So the state of the flag is "pessimistic", as in it may report false
> negatives, but never false positives.
> 
> Reviewed-by: Joe Damato <jdamato@...tly.com>
> Reviewed-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>