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    Subject[PATCH 23/33] netvm: skb processing
    In order to make sure emergency packets receive all memory needed to proceed
    ensure processing of emergency SKBs happens under PF_MEMALLOC.

    Use the (new) sk_backlog_rcv() wrapper to ensure this for backlog processing.

    Skip taps, since those are user-space again.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/net/sock.h | 5 +++++
    net/core/dev.c | 44 ++++++++++++++++++++++++++++++++++++++------
    net/core/sock.c | 18 ++++++++++++++++++
    3 files changed, 61 insertions(+), 6 deletions(-)

    Index: linux-2.6/net/core/dev.c
    ===================================================================
    --- linux-2.6.orig/net/core/dev.c
    +++ linux-2.6/net/core/dev.c
    @@ -1976,10 +1976,23 @@ int netif_receive_skb(struct sk_buff *sk
    struct net_device *orig_dev;
    int ret = NET_RX_DROP;
    __be16 type;
    + unsigned long pflags = current->flags;
    +
    + /* Emergency skb are special, they should
    + * - be delivered to SOCK_MEMALLOC sockets only
    + * - stay away from userspace
    + * - have bounded memory usage
    + *
    + * Use PF_MEMALLOC as a poor mans memory pool - the grouping kind.
    + * This saves us from propagating the allocation context down to all
    + * allocation sites.
    + */
    + if (skb_emergency(skb))
    + current->flags |= PF_MEMALLOC;

    /* if we've gotten here through NAPI, check netpoll */
    if (netpoll_receive_skb(skb))
    - return NET_RX_DROP;
    + goto out;

    if (!skb->tstamp.tv64)
    net_timestamp(skb);
    @@ -1990,7 +2003,7 @@ int netif_receive_skb(struct sk_buff *sk
    orig_dev = skb_bond(skb);

    if (!orig_dev)
    - return NET_RX_DROP;
    + goto out;

    __get_cpu_var(netdev_rx_stat).total++;

    @@ -2009,6 +2022,9 @@ int netif_receive_skb(struct sk_buff *sk
    }
    #endif

    + if (skb_emergency(skb))
    + goto skip_taps;
    +
    list_for_each_entry_rcu(ptype, &ptype_all, list) {
    if (!ptype->dev || ptype->dev == skb->dev) {
    if (pt_prev)
    @@ -2017,6 +2033,7 @@ int netif_receive_skb(struct sk_buff *sk
    }
    }

    +skip_taps:
    #ifdef CONFIG_NET_CLS_ACT
    if (pt_prev) {
    ret = deliver_skb(skb, pt_prev, orig_dev);
    @@ -2029,19 +2046,31 @@ int netif_receive_skb(struct sk_buff *sk

    if (ret == TC_ACT_SHOT || (ret == TC_ACT_STOLEN)) {
    kfree_skb(skb);
    - goto out;
    + goto unlock;
    }

    skb->tc_verd = 0;
    ncls:
    #endif

    + if (skb_emergency(skb))
    + switch(skb->protocol) {
    + case __constant_htons(ETH_P_ARP):
    + case __constant_htons(ETH_P_IP):
    + case __constant_htons(ETH_P_IPV6):
    + case __constant_htons(ETH_P_8021Q):
    + break;
    +
    + default:
    + goto drop;
    + }
    +
    skb = handle_bridge(skb, &pt_prev, &ret, orig_dev);
    if (!skb)
    - goto out;
    + goto unlock;
    skb = handle_macvlan(skb, &pt_prev, &ret, orig_dev);
    if (!skb)
    - goto out;
    + goto unlock;

    type = skb->protocol;
    list_for_each_entry_rcu(ptype, &ptype_base[ntohs(type)&15], list) {
    @@ -2056,6 +2085,7 @@ ncls:
    if (pt_prev) {
    ret = pt_prev->func(skb, skb->dev, pt_prev, orig_dev);
    } else {
    +drop:
    kfree_skb(skb);
    /* Jamal, now you will not able to escape explaining
    * me how you were going to use this. :-)
    @@ -2063,8 +2093,10 @@ ncls:
    ret = NET_RX_DROP;
    }

    -out:
    +unlock:
    rcu_read_unlock();
    +out:
    + tsk_restore_flags(current, pflags, PF_MEMALLOC);
    return ret;
    }

    Index: linux-2.6/include/net/sock.h
    ===================================================================
    --- linux-2.6.orig/include/net/sock.h
    +++ linux-2.6/include/net/sock.h
    @@ -523,8 +523,13 @@ static inline void sk_add_backlog(struct
    skb->next = NULL;
    }

    +extern int __sk_backlog_rcv(struct sock *sk, struct sk_buff *skb);
    +
    static inline int sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)
    {
    + if (skb_emergency(skb))
    + return __sk_backlog_rcv(sk, skb);
    +
    return sk->sk_backlog_rcv(sk, skb);
    }

    Index: linux-2.6/net/core/sock.c
    ===================================================================
    --- linux-2.6.orig/net/core/sock.c
    +++ linux-2.6/net/core/sock.c
    @@ -319,6 +319,24 @@ int sk_clear_memalloc(struct sock *sk)
    }
    EXPORT_SYMBOL_GPL(sk_clear_memalloc);

    +#ifdef CONFIG_NETVM
    +int __sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)
    +{
    + int ret;
    + unsigned long pflags = current->flags;
    +
    + /* these should have been dropped before queueing */
    + BUG_ON(!sk_has_memalloc(sk));
    +
    + current->flags |= PF_MEMALLOC;
    + ret = sk->sk_backlog_rcv(sk, skb);
    + tsk_restore_flags(current, pflags, PF_MEMALLOC);
    +
    + return ret;
    +}
    +EXPORT_SYMBOL(__sk_backlog_rcv);
    +#endif
    +
    static int sock_set_timeout(long *timeo_p, char __user *optval, int optlen)
    {
    struct timeval tv;
    --

    -
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