packet: don't unconditionally schedule() in case of MSG_DONTWAIT (87a2fd28) · Commits · 戴 / test

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>

net/packet/af_packet.c

+6 −7

Original line number	Diff line number	Diff line
		@@ -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;
		@@ -2199,8 +2200,8 @@ static int tpacket_snd(struct packet_sock po, struct msghdr msg)
		do {
		ph = packet_current_frame(po, &po->tx_ring,
		TP_STATUS_SEND_REQUEST);

		if (unlikely(ph == NULL)) {
		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;

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