netdev - Re: [PATCH net-next v3 5/7] mld: convert ifmcaddr6 to RCU

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Date:   Mon, 29 Mar 2021 21:56:32 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Taehee Yoo <ap420073@...il.com>, netdev@...r.kernel.org,
        davem@...emloft.net, kuba@...nel.org
Cc:     jwi@...ux.ibm.com, kgraul@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, borntraeger@...ibm.com,
        mareklindner@...mailbox.ch, sw@...onwunderlich.de, a@...table.cc,
        sven@...fation.org, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        linux-s390@...r.kernel.org, b.a.t.m.a.n@...ts.open-mesh.org
Subject: Re: [PATCH net-next v3 5/7] mld: convert ifmcaddr6 to RCU



On 3/25/21 5:16 PM, Taehee Yoo wrote:
> The ifmcaddr6 has been protected by inet6_dev->lock(rwlock) so that
> the critical section is atomic context. In order to switch this context,
> changing locking is needed. The ifmcaddr6 actually already protected by
> RTNL So if it's converted to use RCU, its control path context can be
> switched to sleepable.
>

I do not really understand the changelog.

You wanted to convert from RCU to RTNL, right ?

Also :

> @@ -571,13 +573,9 @@ int ip6_mc_msfget(struct sock *sk, struct group_filter *gsf,
>  	if (!ipv6_addr_is_multicast(group))
>  		return -EINVAL;
>  
> -	rcu_read_lock();
> -	idev = ip6_mc_find_dev_rcu(net, group, gsf->gf_interface);
> -
> -	if (!idev) {
> -		rcu_read_unlock();
> +	idev = ip6_mc_find_dev_rtnl(net, group, gsf->gf_interface);
> +	if (!idev)
>  		return -ENODEV;
> -	}
>  

I do not see RTNL being acquired before entering ip6_mc_msfget()