net: core: another layer of lists, around PF_MEMALLOC skb handling

First example of a layer splitting the list (rather than merely taking
 individual packets off it).
Involves new list.h function, list_cut_before(), like list_cut_position()
 but cuts on the other side of the given entry.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 36 insertions, 8 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 1e87361df2ab..9aadef976e8c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4784,6 +4784,14 @@ int netif_receive_skb_core(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(netif_receive_skb_core);
 
+static void __netif_receive_skb_list_core(struct list_head *head, bool pfmemalloc)
+{
+	struct sk_buff *skb, *next;
+
+	list_for_each_entry_safe(skb, next, head, list)
+		__netif_receive_skb_core(skb, pfmemalloc);
+}
+
 static int __netif_receive_skb(struct sk_buff *skb)
 {
 	int ret;
@@ -4809,6 +4817,34 @@ static int __netif_receive_skb(struct sk_buff *skb)
 	return ret;
 }
 
+static void __netif_receive_skb_list(struct list_head *head)
+{
+	unsigned long noreclaim_flag = 0;
+	struct sk_buff *skb, *next;
+	bool pfmemalloc = false; /* Is current sublist PF_MEMALLOC? */
+
+	list_for_each_entry_safe(skb, next, head, list) {
+		if ((sk_memalloc_socks() && skb_pfmemalloc(skb)) != pfmemalloc) {
+			struct list_head sublist;
+
+			/* Handle the previous sublist */
+			list_cut_before(&sublist, head, &skb->list);
+			__netif_receive_skb_list_core(&sublist, pfmemalloc);
+			pfmemalloc = !pfmemalloc;
+			/* See comments in __netif_receive_skb */
+			if (pfmemalloc)
+				noreclaim_flag = memalloc_noreclaim_save();
+			else
+				memalloc_noreclaim_restore(noreclaim_flag);
+		}
+	}
+	/* Handle the remaining sublist */
+	__netif_receive_skb_list_core(head, pfmemalloc);
+	/* Restore pflags */
+	if (pfmemalloc)
+		memalloc_noreclaim_restore(noreclaim_flag);
+}
+
 static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
 {
 	struct bpf_prog *old = rtnl_dereference(dev->xdp_prog);
@@ -4843,14 +4879,6 @@ static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
 	return ret;
 }
 
-static void __netif_receive_skb_list(struct list_head *head)
-{
-	struct sk_buff *skb, *next;
-
-	list_for_each_entry_safe(skb, next, head, list)
-		__netif_receive_skb(skb);
-}
-
 static int netif_receive_skb_internal(struct sk_buff *skb)
 {
 	int ret;