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rxrpc: Fix lockup due to no error backoff after ack transmit error 

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: 248f219cb8 ("rxrpc: Rewrite the data and ack handling code")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Howells 2018-11-01 13:39:53 +00:00 committed by David S. Miller
parent 284fb78ed7
commit c7e86acfce
3 changed files with 46 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
net/rxrpc/ar-internal.h
View File

@ -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

18
net/rxrpc/call_event.c
View File

@ -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;
}

35
net/rxrpc/output.c
View File

@ -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;