netdev - Re: [PATCH v2 net-next 09/15] ipv6: mcast: Don't hold RTNL for MCAST

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Message-ID: <CANn89i+zxB0cq55RLC5MdJLkcbDiWAjZfO5YDDQ8gLrgeERbng@mail.gmail.com>
Date: Thu, 26 Jun 2025 07:44:06 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuni1840@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 09/15] ipv6: mcast: Don't hold RTNL for MCAST_
 socket options.

On Tue, Jun 24, 2025 at 1:26 PM Kuniyuki Iwashima <kuni1840@...il.com> wrote:
>
> From: Kuniyuki Iwashima <kuniyu@...gle.com>
>
> In ip6_mc_source() and ip6_mc_msfilter(), per-socket mld data is
> protected by lock_sock() and inet6_dev->mc_lock is also held for
> some per-interface functions.
>
> ip6_mc_find_dev_rtnl() only depends on RTNL.  If we want to remove
> it, we need to check inet6_dev->dead under mc_lock to close the race
> with addrconf_ifdown(), as mentioned earlier.
>
> Let's do that and drop RTNL for the rest of MCAST_ socket options.
>
> Note that ip6_mc_msfilter() has unnecessary lock dances and they
> are integrated into one to avoid the last-minute error and simplify
> the error handling.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
> ---

Same remark about lack of one READ_ONCE( rt->dst.dev)

Other than that :

Reviewed-by: Eric Dumazet <edumazet@...gle.com>