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VK7AX > LINHAM 18.06.08 01:26l 80 Lines 3226 Bytes #999 (0) @ WW
BID : VK7AX-1806CK
Read: GUEST
Subj: Re: [PATCH]: Consolidate ax25 socket grafting.
Path: IZ3LSV<IK2XDE<DB0RES<DK0WUE<7M3TJZ<ON0BEL<VK7AX
Sent: 080617/2327Z @:VK7AX.#ULV.TAS.AUS.OC #:47475 [Ulverstone] FBB7.00g $:VK7A
From: VK7AX@VK7AX.#ULV.TAS.AUS.OC
To : LINHAM@WW
From: Tihomir Heidelberg - 9a4gl <9a4gl(AT)hamradio.hr>
Date: Tue, 17 Jun 2008 14:11:36 +0200
To: linux-hams(AT)vger.kernel.org
CC: David Miller <davem(AT)davemloft.net>, netdev(AT)vger.kernel.org,
ralf(AT)linux-mips.org
Hi linux-hams,
David Miller wrote:
> The way that listening sockets work in ax25 is that the packet input
> code path creates new socks via ax25_make_new() and attaches them
> to the incoming SKB. This SKB gets queued up into the listening
> socket's receive queue.
>
> When accept()'d the sock gets hooked up to the real parent socket.
> Alternatively, if the listening socket is closed and released, any
> unborn socks stuff up in the receive queue get released.
>
> So during this time period these sockets are unreachable in any
> other way, so no wakeup events nor references to their ->sk_socket
> and ->sk_sleep members can occur. And even if they do, all such
> paths have to make NULL checks.
>
Yes, but...
I would like to direct you attention to one problem existing in ax.25 kernel
since 2.4. If listening socket is closed and its SKB queue is released but
those sockets get weird. Those "unAccepted()" sockets should be destroyed
in ax25_std_heartbeat_expiry, but it will not happen. And there is also a
note about that in ax25_std_timer.c:
/* Magic here: If we listen() and a new link dies before it
is accepted() it isn't 'dead' so doesn't get removed. */
This issue cause ax25d to stop accepting new connections and I had to
restarted ax25d approximately each day and my services were unavailable.
Also netstat -n -l shows invalid source and device for those listening sockets.
It is strange why ax25d's listening socket get weird because of this issue,
but definitely when I solved this bug I do not have problems with ax25d
anymore and my ax25d can run for months without problems.
Actually I didn't fix the bug, I made a hack. In af_ax25.c file,
function ax25_destroy_socket in while loop:
if (ax25->sk != NULL) {
while ((skb = skb_dequeue(&ax25->sk->sk_receive_queue)) != NULL
if (skb->sk != ax25->sk) {
/* A pending connection */
ax25_cb *sax25 = ax25_sk(skb->sk);
/* Queue the unaccepted socket for death */
sock_orphan(skb->sk);
+ /* 9A4GL: hack to release unaccepted sockets */
+ skb->sk->sk_state = TCP_LISTEN;
ax25_start_heartbeat(sax25);
sax25->state = AX25_STATE_0;
}
kfree_skb(skb);
}
skb_queue_purge(&ax25->sk->sk_write_queue);
}
73 de Tihomir, 9a4gl
--
*******************************************************************
ABOVE IS A CROSS POST TO THE PACKET RADIO NETWORK IN AN EFFORT TO
PROMOTE FURTHER INTEREST IN HAM SOFTWARE USING LINUX OPERATING
SYSTEMS AND PACKET RADIO
Courtesy Tony VK7AX VK7AX(AT)VK7AX.#ULV.TAS.AUS.OC
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