netlink: add flow control for memory mapped I/O

Add flow control for memory mapped RX. Since user-space usually doesn't
invoke recvmsg() when using memory mapped I/O, flow control is performed
in netlink_poll(). Dumps are allowed to continue if at least half of the
ring frames are unused.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 61 insertions, 27 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index d120b5d4d86a..2a3e9ba814c4 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -3,6 +3,7 @@
  *
  *              Authors:        Alan Cox <alan@lxorguk.ukuu.org.uk>
  *                              Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
+ *                              Patrick McHardy <kaber@trash.net>
  *
  *              This program is free software; you can redistribute it and/or
  *              modify it under the terms of the GNU General Public License
@@ -110,6 +111,29 @@ static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u
         return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
 }
 
+static void netlink_overrun(struct sock *sk)
+{
+        struct netlink_sock *nlk = nlk_sk(sk);
+
+        if (!(nlk->flags & NETLINK_RECV_NO_ENOBUFS)) {
+                if (!test_and_set_bit(NETLINK_CONGESTED, &nlk_sk(sk)->state)) {
+                        sk->sk_err = ENOBUFS;
+                        sk->sk_error_report(sk);
+                }
+        }
+        atomic_inc(&sk->sk_drops);
+}
+
+static void netlink_rcv_wake(struct sock *sk)
+{
+        struct netlink_sock *nlk = nlk_sk(sk);
+
+        if (skb_queue_empty(&sk->sk_receive_queue))
+                clear_bit(NETLINK_CONGESTED, &nlk->state);
+        if (!test_bit(NETLINK_CONGESTED, &nlk->state))
+                wake_up_interruptible(&nlk->wait);
+}
+
 #ifdef CONFIG_NETLINK_MMAP
 static bool netlink_skb_is_mmaped(const struct sk_buff *skb)
 {
@@ -441,15 +465,48 @@ static void netlink_forward_ring(struct netlink_ring *ring)
         } while (ring->head != head);
 }
 
+static bool netlink_dump_space(struct netlink_sock *nlk)
+{
+        struct netlink_ring *ring = &nlk->rx_ring;
+        struct nl_mmap_hdr *hdr;
+        unsigned int n;
+
+        hdr = netlink_current_frame(ring, NL_MMAP_STATUS_UNUSED);
+        if (hdr == NULL)
+                return false;
+
+        n = ring->head + ring->frame_max / 2;
+        if (n > ring->frame_max)
+                n -= ring->frame_max;
+
+        hdr = __netlink_lookup_frame(ring, n);
+
+        return hdr->nm_status == NL_MMAP_STATUS_UNUSED;
+}
+
 static unsigned int netlink_poll(struct file *file, struct socket *sock,
                                  poll_table *wait)
 {
         struct sock *sk = sock->sk;
         struct netlink_sock *nlk = nlk_sk(sk);
         unsigned int mask;
+        int err;
 
-        if (nlk->cb != NULL && nlk->rx_ring.pg_vec != NULL)
-                netlink_dump(sk);
+        if (nlk->rx_ring.pg_vec != NULL) {
+                /* Memory mapped sockets don't call recvmsg(), so flow control
+                 * for dumps is performed here. A dump is allowed to continue
+                 * if at least half the ring is unused.
+                 */
+                while (nlk->cb != NULL && netlink_dump_space(nlk)) {
+                        err = netlink_dump(sk);
+                        if (err < 0) {
+                                sk->sk_err = err;
+                                sk->sk_error_report(sk);
+                                break;
+                        }
+                }
+                netlink_rcv_wake(sk);
+        }
 
         mask = datagram_poll(file, sock, wait);
 
@@ -623,8 +680,7 @@ static void netlink_ring_set_copied(struct sock *sk, struct sk_buff *skb)
         if (hdr == NULL) {
                 spin_unlock_bh(&sk->sk_receive_queue.lock);
                 kfree_skb(skb);
-                sk->sk_err = ENOBUFS;
-                sk->sk_error_report(sk);
+                netlink_overrun(sk);
                 return;
         }
         netlink_increment_head(ring);
@@ -1329,19 +1385,6 @@ static int netlink_getname(struct socket *sock, struct sockaddr *addr,
         return 0;
 }
 
-static void netlink_overrun(struct sock *sk)
-{
-        struct netlink_sock *nlk = nlk_sk(sk);
-
-        if (!(nlk->flags & NETLINK_RECV_NO_ENOBUFS)) {
-                if (!test_and_set_bit(NETLINK_CONGESTED, &nlk_sk(sk)->state)) {
-                        sk->sk_err = ENOBUFS;
-                        sk->sk_error_report(sk);
-                }
-        }
-        atomic_inc(&sk->sk_drops);
-}
-
 static struct sock *netlink_getsockbyportid(struct sock *ssk, u32 portid)
 {
         struct sock *sock;
@@ -1484,16 +1527,6 @@ static struct sk_buff *netlink_trim(struct sk_buff *skb, gfp_t allocation)
         return skb;
 }
 
-static void netlink_rcv_wake(struct sock *sk)
-{
-        struct netlink_sock *nlk = nlk_sk(sk);
-
-        if (skb_queue_empty(&sk->sk_receive_queue))
-                clear_bit(NETLINK_CONGESTED, &nlk->state);
-        if (!test_bit(NETLINK_CONGESTED, &nlk->state))
-                wake_up_interruptible(&nlk->wait);
-}
-
 static int netlink_unicast_kernel(struct sock *sk, struct sk_buff *skb,
                                   struct sock *ssk)
 {
@@ -1597,6 +1630,7 @@ struct sk_buff *netlink_alloc_skb(struct sock *ssk, unsigned int size,
 err2:
         kfree_skb(skb);
         spin_unlock_bh(&sk->sk_receive_queue.lock);
+        netlink_overrun(sk);
 err1:
         sock_put(sk);
         return NULL;