Re: [PATCH 3/6] netfilter: ctnetlink: use GFP_ATOMIC in all allocations

[Eric Dumazet <eric.dumazet@gmail.com>]

On Tue, 2012-03-06 at 12:22 +0100, pablo@netfilter.org wrote:
> From: Pablo Neira Ayuso <pablo@netfilter.org>
> 
> All ctnetlink operations are invoked inside rcu_read_lock
> (see net/netfilter/nfnetlink.c).
> 
> Allocations have to be atomic, as RCU requires.
> 
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
> ---
>  net/netfilter/nf_conntrack_netlink.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
> index 1068769..867843f 100644
> --- a/net/netfilter/nf_conntrack_netlink.c
> +++ b/net/netfilter/nf_conntrack_netlink.c
> @@ -1002,7 +1002,7 @@ ctnetlink_get_conntrack(struct sock *ctnl, struct sk_buff *skb,
>  	ct = nf_ct_tuplehash_to_ctrack(h);
>  
>  	err = -ENOMEM;
> -	skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
> +	skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
>  	if (skb2 == NULL) {
>  		nf_ct_put(ct);
>  		return -ENOMEM;
> @@ -1865,7 +1865,7 @@ ctnetlink_get_expect(struct sock *ctnl, struct sk_buff *skb,
>  	}
>  
>  	err = -ENOMEM;
> -	skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
> +	skb2 = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
>  	if (skb2 == NULL) {
>  		nf_ct_expect_put(exp);
>  		goto out;

This cant be right.

Really this must be kept as GFP_KERNEL allocations.

Only if .call_rcu member is used in place of .call rcu_read_lock() is
held instead of nfnl_lock().

You should take a look at all GFP_ATOMIC uses in
net/netfilter/nf_conntrack_netlink.c and check if they can be GFP_KERNEL
instead.