Date:	21 Mar 2007 11:26:06 -0000
From:	"Samuel Ortiz" <samuel@...tiz.org>
To:	gl@...-ac.de
CC:	"irda-users@...ts.sourceforge.net" <irda-users@...ts.sourceforge.net>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [irda-users] [2.6.20-rt8] "Neighbour table overflow."


On 3/21/2007, "Guennadi Liakhovetski" <gl@...-ac.de> wrote:

>(Short recap for newly added to cc: netdev: I'm seeing an skb leak in
>2.6.20 during an IrDA IrNET+ppp UDP test with periodic connection
>disruptions)
>
>On Wed, 21 Mar 2007, Guennadi Liakhovetski wrote:
>
>> On Tue, 20 Mar 2007, Guennadi Liakhovetski wrote:
>>
>> Ok, looks like all leaked skbuffs come from ip_append_data(), like this:
>>
>> (sock_alloc_send_skb+0x2c8/0x2e4)
>> (ip_append_data+0x7fc/0xa80)
>> (udp_sendmsg+0x248/0x68c)
>> (inet_sendmsg+0x60/0x64)
>> (sock_sendmsg+0xb4/0xe4)
>>  r4 = C3CB4960
>> (sys_sendto+0xc8/0xf0)
>>  r4 = 00000000
>> (sys_socketcall+0x168/0x1f0)
>> (ret_fast_syscall+0x0/0x2c)
>
>This call to sock_alloc_send_skb() in ip_append_data() is not from the
>inlined ip_ufo_append_data(), it is here:
>
> 			/* The last fragment gets additional space at tail.
> 			 * Note, with MSG_MORE we overallocate on fragments,
> 			 * because we have no idea what fragment will be
> 			 * the last.
> 			 */
> 			if (datalen == length + fraggap)
> 				alloclen += rt->u.dst.trailer_len;
>
> 			if (transhdrlen) {
> 				skb = sock_alloc_send_skb(sk,
> 						alloclen + hh_len + 15,
> 						(flags & MSG_DONTWAIT), &err);
> 			} else {
>
>Then, I traced a couple of paths how such a skbuff, coming down from
>ip_append_data() and allocated above get freed (when they do):
>
>[<c0182380>] (__kfree_skb+0x0/0x170) from [<c0182514>] (kfree_skb+0x24/0x50)
>  r5 = C332BC00  r4 = C332BC00
>[<c01824f0>] (kfree_skb+0x0/0x50) from [<bf0fac58>] (irlap_update_nr_received+0x94/0xc8 [irda])
>[<bf0fabc4>] (irlap_update_nr_received+0x0/0xc8 [irda]) from [<bf0fda98>] (irlap_state_nrm_p+0x530/0x7c0 [irda])
>  r7 = 00000001  r6 = C0367EC0  r5 = C332BC00  r4 = 00000000
>[<bf0fd568>] (irlap_state_nrm_p+0x0/0x7c0 [irda]) from [<bf0fbd90>] (irlap_do_event+0x68/0x18c [irda])
>[<bf0fbd28>] (irlap_do_event+0x0/0x18c [irda]) from [<bf1008cc>] (irlap_driver_rcv+0x1f0/0xd38 [irda])
>[<bf1006dc>] (irlap_driver_rcv+0x0/0xd38 [irda]) from [<c01892c0>] (netif_receive_skb+0x244/0x338)
>[<c018907c>] (netif_receive_skb+0x0/0x338) from [<c0189468>] (process_backlog+0xb4/0x194)
>[<c01893b4>] (process_backlog+0x0/0x194) from [<c01895f8>] (net_rx_action+0xb0/0x210)
>[<c0189548>] (net_rx_action+0x0/0x210) from [<c0042f7c>] (ksoftirqd+0x108/0x1cc)
>[<c0042e74>] (ksoftirqd+0x0/0x1cc) from [<c0053614>] (kthread+0x10c/0x138)
>[<c0053508>] (kthread+0x0/0x138) from [<c003f918>] (do_exit+0x0/0x8b0)
>  r8 = 00000000  r7 = 00000000  r6 = 00000000  r5 = 00000000
>  r4 = 00000000
This is the IrDA RX path, so I doubt the corresponding skb ever got
through
ip_append_data(). The skb was allocated by your HW driver upon packet
reception, then queued to the net input queue, and finally passed to the
IrDA stack. Are you sure your tracing is correct ?


>and
>
>[<c0182380>] (__kfree_skb+0x0/0x170) from [<c0182514>] (kfree_skb+0x24/0x50)
>  r5 = C03909E0  r4 = C1A97400
>[<c01824f0>] (kfree_skb+0x0/0x50) from [<c0199bf8>] (pfifo_fast_enqueue+0xb4/0xd0)
>[<c0199b44>] (pfifo_fast_enqueue+0x0/0xd0) from [<c0188c30>] (dev_queue_xmit+0x17c/0x25c)
>  r8 = C1A2DCE0  r7 = FFFFFFF4  r6 = C3393114  r5 = C03909E0
>  r4 = C3393000
>[<c0188ab4>] (dev_queue_xmit+0x0/0x25c) from [<c01a7c18>] (ip_output+0x150/0x254)
>  r7 = C3717120  r6 = C03909E0  r5 = 00000000  r4 = C1A2DCE0
>[<c01a7ac8>] (ip_output+0x0/0x254) from [<c01a93d0>] (ip_push_pending_frames+0x368/0x4d4)
>[<c01a9068>] (ip_push_pending_frames+0x0/0x4d4) from [<c01c6954>] (udp_push_pending_frames+0x14c/0x310)
>[<c01c6808>] (udp_push_pending_frames+0x0/0x310) from [<c01c70d8>] (udp_sendmsg+0x5c0/0x690)
>[<c01c6b18>] (udp_sendmsg+0x0/0x690) from [<c01ceafc>] (inet_sendmsg+0x60/0x64)
>[<c01cea9c>] (inet_sendmsg+0x0/0x64) from [<c017c970>] (sock_sendmsg+0xb4/0xe4)
>  r7 = C2CEFDF4  r6 = 00000064  r5 = C2CEFEA8  r4 = C3C94080
>[<c017c8bc>] (sock_sendmsg+0x0/0xe4) from [<c017dd9c>] (sys_sendto+0xc8/0xf0)
>  r7 = 00000064  r6 = C3571580  r5 = C2CEFEC4  r4 = 00000000
>[<c017dcd4>] (sys_sendto+0x0/0xf0) from [<c017e654>] (sys_socketcall+0x168/0x1f0)
>[<c017e4ec>] (sys_socketcall+0x0/0x1f0) from [<c001ff40>] (ret_fast_syscall+0x0/0x2c)
>  r5 = 00415344  r4 = 00000000
This one is on the TX path, yes. However it got dropped and freed because
your TX queue was full. Any idea in which situation does that happen ?


>I would be greatful for any hints how I can identify which skbuff's get
>lost and why, and where and who should free them.
You're seeing skb leaks when cutting the ppp connection periodically,
right ?
Do you such leaks when not cutting the ppp connection ?
If not, could you send me a kernel trace (with irda debug set to 5) when
the ppp connection is shut down ? It would narrow down the problem a bit.
I'm quite sure the leak is in the IrDA code rather than in the ppp or
ipv4
one, hence the need for full irda debug...

Cheers,
Samuel.

>I am not subscribed to netdev, please keep in cc.
>
>Thanks
>Guennadi
>---------------------------------
>Guennadi Liakhovetski, Ph.D.
>DSA Daten- und Systemtechnik GmbH
>Pascalstr. 28
>D-52076 Aachen
>Germany
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