packet: don't unconditionally schedule() in case of MSG_DONTWAIT

In tpacket_snd(), when we've discovered a first frame that is
not in status TP_STATUS_SEND_REQUEST, and return a NULL buffer,
we exit the send routine in case of MSG_DONTWAIT, since we've
finished traversing the mmaped send ring buffer and don't care
about pending frames.

While doing so, we still unconditionally call an expensive
schedule() in the packet_current_frame() "error" path, which
is unnecessary in this case since it's enough to just quit
the function.

Also, in case MSG_DONTWAIT is not set, we should rather test
for need_resched() first and do schedule() only if necessary
since meanwhile pending frames could already have finished
processing and called skb destructor.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 7 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 85bb38cb56fd..d5495d87f399 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2156,6 +2156,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
         int err, reserve = 0;
         void *ph;
         struct sockaddr_ll *saddr = (struct sockaddr_ll *)msg->msg_name;
+        bool need_wait = !(msg->msg_flags & MSG_DONTWAIT);
         int tp_len, size_max;
         unsigned char *addr;
         int len_sum = 0;
@@ -2198,10 +2199,10 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 
         do {
                 ph = packet_current_frame(po, &po->tx_ring,
-                                TP_STATUS_SEND_REQUEST);
-
+                                          TP_STATUS_SEND_REQUEST);
                 if (unlikely(ph == NULL)) {
-                        schedule();
+                        if (need_wait && need_resched())
+                                schedule();
                         continue;
                 }
 
@@ -2255,10 +2256,8 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
                 }
                 packet_increment_head(&po->tx_ring);
                 len_sum += tp_len;
-        } while (likely((ph != NULL) ||
-                        ((!(msg->msg_flags & MSG_DONTWAIT)) &&
-                         (atomic_read(&po->tx_ring.pending))))
-                );
+        } while (likely((ph != NULL) || (need_wait &&
+                                         atomic_read(&po->tx_ring.pending))));
 
         err = len_sum;
         goto out_put;