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Commit 87a2fd28 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

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: default avatarDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 902fefb8

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;