On Sep 3, 2012, at 10:27 AM, Thomas Graf <tgraf@xxxxxxx> wrote:
SCTP charges wmem_alloc via sctp_set_owner_w() in sctp_sendmsg() and
via
skb_set_owner_w() in sctp_packet_transmit(). If a sender runs out of
sndbuf it will sleep in sctp_wait_for_sndbuf() and expects to be
waken up
by __sctp_write_space().
Buffer space charged via sctp_set_owner_w() is released in sctp_wfree
()
which calls __sctp_write_space() directly.
Buffer space charged via skb_set_owner_w() is released via sock_wfree
()
which calls sk->sk_write_space() _if_ SOCK_USE_WRITE_QUEUE is not set.
sctp_endpoint_init() sets SOCK_USE_WRITE_QUEUE on all sockets.
Therefore if sctp_packet_transmit() manages to queue up more than
sndbuf
bytes, sctp_wait_for_sndbuf() will never be woken up again unless it
is
interrupted by a signal.
This could be fixed by clearing the SOCK_USE_WRITE_QUEUE flag but ...
Charging for the data twice does not make sense in the first place, it
leads to overcharging sndbuf by a factor 2. Therefore this patch only
charges a single byte in wmem_alloc when transmitting an SCTP packet
to
ensure that the socket stays alive until the packet has been released.
This means that control chunks are no longer accounted for in
wmem_alloc
which I believe is not a problem as skb->truesize will typically lead
to overcharging anyway and thus compensates for any control overhead.
Acked-by: Vlad Yasevich <vyasevich@xxxxxxxxx>
-vlad
Signed-off-by: Thomas Graf <tgraf@xxxxxxx>
CC: Vlad Yasevich <vyasevic@xxxxxxxxxx>
CC: Neil Horman <nhorman@xxxxxxxxxxxxx>
CC: David Miller <davem@xxxxxxxxxxxxx>
---
net/sctp/output.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/net/sctp/output.c b/net/sctp/output.c
index 838e18b..be50aa2 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -364,6 +364,25 @@ finish:
return retval;
}
+static void sctp_packet_release_owner(struct sk_buff *skb)
+{
+ sk_free(skb->sk);
+}
+
+static void sctp_packet_set_owner_w(struct sk_buff *skb, struct
sock *sk)
+{
+ skb_orphan(skb);
+ skb->sk = sk;
+ skb->destructor = sctp_packet_release_owner;
+
+ /*
+ * The data chunks have already been accounted for in
sctp_sendmsg(),
+ * therefore only reserve a single byte to keep socket around
until
+ * the packet has been transmitted.
+ */
+ atomic_inc(&sk->sk_wmem_alloc);
+}
+
/* All packets are sent to the network through this function from
* sctp_outq_tail().
*
@@ -405,7 +424,7 @@ int sctp_packet_transmit(struct sctp_packet
*packet)
/* Set the owning socket so that we know where to get the
* destination IP address.
*/
- skb_set_owner_w(nskb, sk);
+ sctp_packet_set_owner_w(nskb, sk);
if (!sctp_transport_dst_check(tp)) {
sctp_transport_route(tp, NULL, sctp_sk(sk));
--
1.7.11.4
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