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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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