lkml.org 
[lkml]   [2018]   [Nov]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH net] rxrpc: Fix lockup due to no error backoff after ack transmit error
From
Date
If the network becomes (partially) unavailable, say by disabling IPv6, the
background ACK transmission routine can get itself into a tizzy by
proposing immediate ACK retransmission. Since we're in the call event
processor, that happens immediately without returning to the workqueue
manager.

The condition should clear after a while when either the network comes back
or the call times out.

Fix this by:

(1) When re-proposing an ACK on failed Tx, don't schedule it immediately.
This will allow a certain amount of time to elapse before we try
again.

(2) Enforce a return to the workqueue manager after a certain number of
iterations of the call processing loop.

(3) Add a backoff delay that increases the delay on deferred ACKs by a
jiffy per failed transmission to a limit of HZ. The backoff delay is
cleared on a successful return from kernel_sendmsg().

(4) Cancel calls immediately if the opening sendmsg fails. The layer
above can arrange retransmission or rotate to another server.

Fixes: 248f219cb8bc ("rxrpc: Rewrite the data and ack handling code")
Signed-off-by: David Howells <dhowells@redhat.com>
---

net/rxrpc/ar-internal.h | 1 +
net/rxrpc/call_event.c | 18 ++++++++++++++----
net/rxrpc/output.c | 35 +++++++++++++++++++++++++++++++----
3 files changed, 46 insertions(+), 8 deletions(-)

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 382196e57a26..bc628acf4f4f 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -611,6 +611,7 @@ struct rxrpc_call {
* not hard-ACK'd packet follows this.
*/
rxrpc_seq_t tx_top; /* Highest Tx slot allocated. */
+ u16 tx_backoff; /* Delay to insert due to Tx failure */

/* TCP-style slow-start congestion control [RFC5681]. Since the SMSS
* is fixed, we keep these numbers in terms of segments (ie. DATA
diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index 8e7434e92097..468efc3660c0 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -123,6 +123,7 @@ static void __rxrpc_propose_ACK(struct rxrpc_call *call, u8 ack_reason,
else
ack_at = expiry;

+ ack_at += READ_ONCE(call->tx_backoff);
ack_at += now;
if (time_before(ack_at, call->ack_at)) {
WRITE_ONCE(call->ack_at, ack_at);
@@ -311,6 +312,7 @@ void rxrpc_process_call(struct work_struct *work)
container_of(work, struct rxrpc_call, processor);
rxrpc_serial_t *send_ack;
unsigned long now, next, t;
+ unsigned int iterations = 0;

rxrpc_see_call(call);

@@ -319,6 +321,11 @@ void rxrpc_process_call(struct work_struct *work)
call->debug_id, rxrpc_call_states[call->state], call->events);

recheck_state:
+ /* Limit the number of times we do this before returning to the manager */
+ iterations++;
+ if (iterations > 5)
+ goto requeue;
+
if (test_and_clear_bit(RXRPC_CALL_EV_ABORT, &call->events)) {
rxrpc_send_abort_packet(call);
goto recheck_state;
@@ -447,13 +454,16 @@ void rxrpc_process_call(struct work_struct *work)
rxrpc_reduce_call_timer(call, next, now, rxrpc_timer_restart);

/* other events may have been raised since we started checking */
- if (call->events && call->state < RXRPC_CALL_COMPLETE) {
- __rxrpc_queue_call(call);
- goto out;
- }
+ if (call->events && call->state < RXRPC_CALL_COMPLETE)
+ goto requeue;

out_put:
rxrpc_put_call(call, rxrpc_call_put);
out:
_leave("");
+ return;
+
+requeue:
+ __rxrpc_queue_call(call);
+ goto out;
}
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 189418888839..736aa9281100 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -34,6 +34,21 @@ struct rxrpc_abort_buffer {

static const char rxrpc_keepalive_string[] = "";

+/*
+ * Increase Tx backoff on transmission failure and clear it on success.
+ */
+static void rxrpc_tx_backoff(struct rxrpc_call *call, int ret)
+{
+ if (ret < 0) {
+ u16 tx_backoff = READ_ONCE(call->tx_backoff);
+
+ if (tx_backoff < HZ)
+ WRITE_ONCE(call->tx_backoff, tx_backoff + 1);
+ } else {
+ WRITE_ONCE(call->tx_backoff, 0);
+ }
+}
+
/*
* Arrange for a keepalive ping a certain time after we last transmitted. This
* lets the far side know we're still interested in this call and helps keep
@@ -210,6 +225,7 @@ int rxrpc_send_ack_packet(struct rxrpc_call *call, bool ping,
else
trace_rxrpc_tx_packet(call->debug_id, &pkt->whdr,
rxrpc_tx_point_call_ack);
+ rxrpc_tx_backoff(call, ret);

if (call->state < RXRPC_CALL_COMPLETE) {
if (ret < 0) {
@@ -218,7 +234,7 @@ int rxrpc_send_ack_packet(struct rxrpc_call *call, bool ping,
rxrpc_propose_ACK(call, pkt->ack.reason,
ntohs(pkt->ack.maxSkew),
ntohl(pkt->ack.serial),
- true, true,
+ false, true,
rxrpc_propose_ack_retry_tx);
} else {
spin_lock_bh(&call->lock);
@@ -300,7 +316,7 @@ int rxrpc_send_abort_packet(struct rxrpc_call *call)
else
trace_rxrpc_tx_packet(call->debug_id, &pkt.whdr,
rxrpc_tx_point_call_abort);
-
+ rxrpc_tx_backoff(call, ret);

rxrpc_put_connection(conn);
return ret;
@@ -413,6 +429,7 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, struct sk_buff *skb,
else
trace_rxrpc_tx_packet(call->debug_id, &whdr,
rxrpc_tx_point_call_data_nofrag);
+ rxrpc_tx_backoff(call, ret);
if (ret == -EMSGSIZE)
goto send_fragmentable;

@@ -445,9 +462,18 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, struct sk_buff *skb,
rxrpc_reduce_call_timer(call, expect_rx_by, nowj,
rxrpc_timer_set_for_normal);
}
- }

- rxrpc_set_keepalive(call);
+ rxrpc_set_keepalive(call);
+ } else {
+ /* Cancel the call if the initial transmission fails,
+ * particularly if that's due to network routing issues that
+ * aren't going away anytime soon. The layer above can arrange
+ * the retransmission.
+ */
+ if (!test_and_set_bit(RXRPC_CALL_BEGAN_RX_TIMER, &call->flags))
+ rxrpc_set_call_completion(call, RXRPC_CALL_LOCAL_ERROR,
+ RX_USER_ABORT, ret);
+ }

_leave(" = %d [%u]", ret, call->peer->maxdata);
return ret;
@@ -506,6 +532,7 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, struct sk_buff *skb,
else
trace_rxrpc_tx_packet(call->debug_id, &whdr,
rxrpc_tx_point_call_data_frag);
+ rxrpc_tx_backoff(call, ret);

up_write(&conn->params.local->defrag_sem);
goto done;
\
 
 \ /
  Last update: 2018-11-01 14:41    [W:0.042 / U:1.044 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site