netdev - Re: [RFC 5/7] net: Add allocation flag to rtnl

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Message-ID: <1467946591.1273.45.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Fri, 08 Jul 2016 04:56:31 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Masashi Honma <masashi.honma@...il.com>
Cc:	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	linux-wireless@...r.kernel.org, linux-rdma@...r.kernel.org,
	linux-audit@...hat.com, cluster-devel@...hat.com,
	davem@...emloft.net, johannes@...solutions.net,
	pablo@...filter.org, kaber@...sh.net, kadlec@...ckhole.kfki.hu,
	dledford@...hat.com, sean.hefty@...el.com,
	hal.rosenstock@...il.com, paul@...l-moore.com, eparis@...hat.com,
	zbr@...emap.net, pshelar@...ira.com, ccaulfie@...hat.com,
	teigland@...hat.com, bsingharora@...il.com
Subject: Re: [RFC 5/7] net: Add allocation flag to rtnl_unicast()

On Wed, 2016-07-06 at 09:28 +0900, Masashi Honma wrote:
> Signed-off-by: Masashi Honma <masashi.honma@...il.com>
> ---


> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index a1f6b7b..2b0b994 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -628,7 +628,7 @@ static int inet6_netconf_get_devconf(struct sk_buff *in_skb,
>  		kfree_skb(skb);
>  		goto errout;
>  	}
> -	err = rtnl_unicast(skb, net, NETLINK_CB(in_skb).portid);
> +	err = rtnl_unicast(skb, net, NETLINK_CB(in_skb).portid, GFP_ATOMIC);
>  errout:
>  	return err;
>  }
> @@ -4824,7 +4824,7 @@ static int inet6_rtm_getaddr(struct sk_buff *in_skb, struct nlmsghdr *nlh)
>  		kfree_skb(skb);
>  		goto errout_ifa;
>  	}
> -	err = rtnl_unicast(skb, net, NETLINK_CB(in_skb).portid);
> +	err = rtnl_unicast(skb, net, NETLINK_CB(in_skb).portid, GFP_KERNEL);
>  errout_ifa:
>  	in6_ifa_put(ifa);
>  errout:


Managing to mix GFP_ATOMIC and GFP_KERNEL almost randomly as you did in
this patch is definitely not good.

Further more, RTNL is a mutex, held in control path, designed to allow
schedules and waiting for memory under pressure.

We do not want to encourage GFP_ATOMIC usage in control path.

Your patch series gives the wrong signal to developers.

I will send a patch against net/ipv4/devinet.c so that we remove
GFP_ATOMIC usage there.