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    Subject[PATCH -mmotm 21/30] netvm: skb processing
    From 15437174f171e197ecdfa5fe71ae89334bb58fd2 Mon Sep 17 00:00:00 2001
    From: Xiaotian Feng <dfeng@redhat.com>
    Date: Tue, 13 Jul 2010 13:07:28 +0800
    Subject: [PATCH 21/30] 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>
    Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
    Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
    ---
    include/net/sock.h | 5 ++++
    net/core/dev.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++---
    net/core/sock.c | 16 +++++++++++++++
    3 files changed, 72 insertions(+), 4 deletions(-)

    diff --git a/include/net/sock.h b/include/net/sock.h
    index ac87f6f..aadf15c 100644
    --- a/include/net/sock.h
    +++ b/include/net/sock.h
    @@ -680,8 +680,13 @@ static inline __must_check int sk_add_backlog(struct sock *sk, struct sk_buff *s
    return 0;
    }

    +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);
    }

    diff --git a/net/core/dev.c b/net/core/dev.c
    index e85cc5f..7169b9b 100644
    --- a/net/core/dev.c
    +++ b/net/core/dev.c
    @@ -2801,6 +2801,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
    struct net_device *orig_or_bond;
    int ret = NET_RX_DROP;
    __be16 type;
    + unsigned long pflags = current->flags;

    if (!netdev_tstamp_prequeue)
    net_timestamp_check(skb);
    @@ -2808,9 +2809,21 @@ static int __netif_receive_skb(struct sk_buff *skb)
    if (vlan_tx_tag_present(skb) && vlan_hwaccel_do_receive(skb))
    return NET_RX_SUCCESS;

    + /* 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->skb_iif)
    skb->skb_iif = skb->dev->ifindex;
    @@ -2852,6 +2865,9 @@ static int __netif_receive_skb(struct sk_buff *skb)
    }
    #endif

    + if (skb_emergency(skb))
    + goto skip_taps;
    +
    list_for_each_entry_rcu(ptype, &ptype_all, list) {
    if (ptype->dev == null_or_orig || ptype->dev == skb->dev ||
    ptype->dev == orig_dev) {
    @@ -2861,13 +2877,17 @@ static int __netif_receive_skb(struct sk_buff *skb)
    }
    }

    +skip_taps:
    #ifdef CONFIG_NET_CLS_ACT
    skb = handle_ing(skb, &pt_prev, &ret, orig_dev);
    if (!skb)
    - goto out;
    + goto unlock;
    ncls:
    #endif

    + if (!skb_emergency_protocol(skb))
    + goto drop;
    +
    /* Handle special case of bridge or macvlan */
    rx_handler = rcu_dereference(skb->dev->rx_handler);
    if (rx_handler) {
    @@ -2877,7 +2897,7 @@ ncls:
    }
    skb = rx_handler(skb);
    if (!skb)
    - goto out;
    + goto unlock;
    }

    /*
    @@ -2907,6 +2927,7 @@ 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. :-)
    @@ -2914,11 +2935,37 @@ ncls:
    ret = NET_RX_DROP;
    }

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

    +/*
    + * Filter the protocols for which the reserves are adequate.
    + *
    + * Before adding a protocol make sure that it is either covered by the existing
    + * reserves, or add reserves covering the memory need of the new protocol's
    + * packet processing.
    + */
    +static int skb_emergency_protocol(struct sk_buff *skb)
    +{
    + 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:
    + return 0;
    + }
    +
    + return 1;
    +}
    +
    /**
    * netif_receive_skb - process receive buffer from network
    * @skb: buffer to process
    diff --git a/net/core/sock.c b/net/core/sock.c
    index f24560c..dfc2dfe 100644
    --- a/net/core/sock.c
    +++ b/net/core/sock.c
    @@ -322,6 +322,22 @@ int sk_clear_memalloc(struct sock *sk)
    return set;
    }
    EXPORT_SYMBOL_GPL(sk_clear_memalloc);
    +
    +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)
    --
    1.7.1.1


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