net: Don't write to current task flags on every packet received.

Even for non-pfmalloc SKBs, __netif_receive_skb() will do a
tsk_restore_flags() on current unconditionally.

Make __netif_receive_skb() a shim around the existing code, renamed to
__netif_receive_skb_core().  Let __netif_receive_skb() wrap the
__netif_receive_skb_core() call with the task flag modifications, if
necessary.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 28 insertions, 18 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 2f31bf97ba65..f44473696b8b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3457,7 +3457,7 @@ static bool skb_pfmemalloc_protocol(struct sk_buff *skb)
         }
 }
 
-static int __netif_receive_skb(struct sk_buff *skb)
+static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc)
 {
         struct packet_type *ptype, *pt_prev;
         rx_handler_func_t *rx_handler;
@@ -3466,24 +3466,11 @@ static int __netif_receive_skb(struct sk_buff *skb)
         bool deliver_exact = false;
         int ret = NET_RX_DROP;
         __be16 type;
-        unsigned long pflags = current->flags;
 
         net_timestamp_check(!netdev_tstamp_prequeue, skb);
 
         trace_netif_receive_skb(skb);
 
-        /*
-         * PFMEMALLOC skbs are special, they should
-         * - be delivered to SOCK_MEMALLOC sockets only
-         * - stay away from userspace
-         * - have bounded memory usage
-         *
-         * Use PF_MEMALLOC as this saves us from propagating the allocation
-         * context down to all allocation sites.
-         */
-        if (sk_memalloc_socks() && skb_pfmemalloc(skb))
-                current->flags |= PF_MEMALLOC;
-
         /* if we've gotten here through NAPI, check netpoll */
         if (netpoll_receive_skb(skb))
                 goto out;
@@ -3517,7 +3504,7 @@ another_round:
         }
 #endif
 
-        if (sk_memalloc_socks() && skb_pfmemalloc(skb))
+        if (pfmemalloc)
                 goto skip_taps;
 
         list_for_each_entry_rcu(ptype, &ptype_all, list) {
@@ -3536,8 +3523,7 @@ skip_taps:
 ncls:
 #endif
 
-        if (sk_memalloc_socks() && skb_pfmemalloc(skb)
-                                && !skb_pfmemalloc_protocol(skb))
+        if (pfmemalloc && !skb_pfmemalloc_protocol(skb))
                 goto drop;
 
         if (vlan_tx_tag_present(skb)) {
@@ -3607,7 +3593,31 @@ drop:
 unlock:
         rcu_read_unlock();
 out:
-        tsk_restore_flags(current, pflags, PF_MEMALLOC);
+        return ret;
+}
+
+static int __netif_receive_skb(struct sk_buff *skb)
+{
+        int ret;
+
+        if (sk_memalloc_socks() && skb_pfmemalloc(skb)) {
+                unsigned long pflags = current->flags;
+
+                /*
+                 * PFMEMALLOC skbs are special, they should
+                 * - be delivered to SOCK_MEMALLOC sockets only
+                 * - stay away from userspace
+                 * - have bounded memory usage
+                 *
+                 * Use PF_MEMALLOC as this saves us from propagating the allocation
+                 * context down to all allocation sites.
+                 */
+                current->flags |= PF_MEMALLOC;
+                ret = __netif_receive_skb_core(skb, true);
+                tsk_restore_flags(current, pflags, PF_MEMALLOC);
+        } else
+                ret = __netif_receive_skb_core(skb, false);
+
         return ret;
 }