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Message-ID: <1380776250.19002.147.camel@edumazet-glaptop.roam.corp.google.com>
Subject: Re: [PATCH net-next] fix unsafe set_memory_rw from softirq
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Alexei Starovoitov <ast@plumgrid.com>
Cc: "David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        James Morris <jmorris@namei.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Patrick McHardy <kaber@trash.net>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Daniel Borkmann <dborkman@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Xi Wang <xi.wang@gmail.com>, x86@kernel.org,
        Eric Dumazet <edumazet@google.com>, linux-kernel@vger.kernel.org,
        Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Wed, 02 Oct 2013 21:57:30 -0700
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On Wed, 2013-10-02 at 21:53 -0700, Eric Dumazet wrote:
> On Wed, 2013-10-02 at 21:44 -0700, Alexei Starovoitov wrote:
> 
> > I think ifdef config_x86 is a bit ugly inside struct sk_filter, but
> > don't mind whichever way.
> 
> Its not fair to make sk_filter bigger, because it means that simple (non
> JIT) filter might need an extra cache line.
> 
> You could presumably use the following layout instead :
> 
> struct sk_filter
> {
>         atomic_t                refcnt;
>         struct rcu_head         rcu;
> 	struct work_struct      work;
> 
>         unsigned int            len ____cacheline_aligned;    /* Number of filter blocks */
>         unsigned int            (*bpf_func)(const struct sk_buff *skb,
>                                             const struct sock_filter *filter);
>         struct sock_filter      insns[0];
> };

And since @len is not used by sk_run_filter() use :

struct sk_filter {
        atomic_t                refcnt;
	int 			len; /* number of filter blocks */
        struct rcu_head         rcu;
        struct work_struct      work;

        unsigned int            (*bpf_func)(const struct sk_buff *skb,
                                            const struct sock_filter *filter) ____cacheline_aligned;
        struct sock_filter      insns[0];
};