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From: Jarek Poplawski on 6 Jan 2010 04:20
On Wed, Jan 06, 2010 at 07:22:08AM +0000, Jarek Poplawski wrote:
> On Tue, Jan 05, 2010 at 09:36:28PM -0500, Michael Breuer wrote:
> > Is it possible that this patch is causing the transmission to
> > momentarily halt such that the overall utilization appears low at the
> > time I see the interrupt errors, vs. the other patch which perhaps
> > doesn't interrupt the traffic flow quite so much?
>
> Yes, without this patch xmit could be stopped earlier on some kind of
> errors, with retransmit of the last message possible. On the other
> hand, other dev_queue_xmit() (negative) errors, are ignored. So this
> place could be still improved by adding proper err handling (or
> removing getting err return from dev_queue_xmit() at all).

On the other hand, returning just this one net_xmit_errno() would be
consistent with non-MMAP sendmsg, so here is an alternative version
for testing.

Thanks,
Jarek P.

-----------------> (alternative #2)

tpacket_snd() can change and kfree an skb after dev_queue_xmit(),
which is illegal.

With debugging by: Stephen Hemminger <shemminger(a)linux-foundation.org>

Reported-by: Michael Breuer <mbreuer(a)majjas.com>
Signed-off-by: Jarek Poplawski <jarkao2(a)gmail.com>
---

net/packet/af_packet.c | 8 +++-----
1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index e0516a2..aba2049 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1021,9 +1021,10 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)

status = TP_STATUS_SEND_REQUEST;
err = dev_queue_xmit(skb);
- if (unlikely(err > 0 && (err = net_xmit_errno(err)) != 0))
- goto out_xmit;
packet_increment_head(&po->tx_ring);
+ if (unlikely(err > 0 && (err = net_xmit_errno(err)) != 0))
+ goto out_put;
+
len_sum += tp_len;
} while (likely((ph != NULL) ||
((!(msg->msg_flags & MSG_DONTWAIT)) &&
@@ -1033,9 +1034,6 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
err = len_sum;
goto out_put;

-out_xmit:
- skb->destructor = sock_wfree;
- atomic_dec(&po->tx_ring.pending);
out_status:
__packet_set_status(po, ph, status);
kfree_skb(skb);
--
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