netdev - Re: [PATCH net-next v3 1/3] ipv4: support sport, dport and ip_proto in RTM

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Date:   Wed, 16 May 2018 13:30:28 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net-next v3 1/3] ipv4: support sport, dport and ip_proto
 in RTM_GETROUTE

On Wed, May 16, 2018 at 11:37 AM, David Miller <davem@...emloft.net> wrote:
> From: Roopa Prabhu <roopa@...ulusnetworks.com>
> Date: Tue, 15 May 2018 20:55:06 -0700
>
>> +static int inet_rtm_getroute_reply(struct sk_buff *in_skb, struct nlmsghdr *nlh,
>> +                                __be32 dst, __be32 src, struct flowi4 *fl4,
>> +                                struct rtable *rt, struct fib_result *res)
>> +{
>> +     struct net *net = sock_net(in_skb->sk);
>> +     struct rtmsg *rtm = nlmsg_data(nlh);
>> +     u32 table_id = RT_TABLE_MAIN;
>> +     struct sk_buff *skb;
>> +     int err = 0;
>> +
>> +     skb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
>> +     if (!skb)
>> +             return -ENOMEM;
>
> If the caller can use GFP_KERNEL, so can this allocation.

yes, but we hold rcu read lock before calling the reply function for fib result.
I did consider allocating the skb before the read lock..but then the
refactoring (into a separate netlink reply func) would seem
unnecessary.

I am fine with pre-allocating and undoing the refactoring if that works better.