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Date:	Mon, 08 Jan 2007 21:18:48 +0100
From:	Jan Kiszka <jan.kiszka@....de>
To:	Jiri Benc <jbenc@...e.cz>
CC:	netdev@...r.kernel.org, Ivo Van Doorn <ivdoorn@...il.com>,
	rt2400-devel@...ts.sourceforge.net
Subject: Re: d80211: How does TX flow control work?

Jan Kiszka wrote:
> Jan Kiszka wrote:
>> Jiri Benc wrote:
>>> On Wed, 03 Jan 2007 19:10:01 +0100, Jan Kiszka wrote:
>>>> BUG: warning at /usr/src/rt2x00/rt2x00/ieee80211/ieee80211.c:1256/ieee80211_tx()
>>>>  <cfa02245> ieee80211_master_start_xmit+0x105/0x430 [80211]  <c024e35d> __ip_ct_refresh_acct+0x4d/0x60
>>>>  <c024fd11> tcp_packet+0x941/0x970  <c0217442> qdisc_restart+0x92/0x100
>>>>  <c020d43d> dev_queue_xmit+0xbd/0x1a0  <cfa050d8> ieee80211_subif_start_xmit+0x468/0x480 [80211]
>>>>  <c0207dca> skb_clone+0x3a/0x1a0  <c021d16d> nf_hook_slow+0x4d/0xc0
>>>>  <c020d495> dev_queue_xmit+0x115/0x1a0  <c0226a63> ip_output+0x1c3/0x200
>>>>  <c0225740> ip_finish_output+0x0/0x180  <c022628b> ip_queue_xmit+0x36b/0x3b0
>>>>  <c0224130> dst_output+0x0/0x10  <ce9bae7d> usb_hcd_giveback_urb+0x2d/0x60 [usbcore]
>>>>  <c0237da2> tcp_v4_send_check+0x82/0xd0  <c0237da2> tcp_v4_send_check+0x82/0xd0
>>>>  <c0233244> tcp_transmit_skb+0x5e4/0x610  <c0234b36> __tcp_push_pending_frames+0x676/0x740
>>>>  <c0207f81> __alloc_skb+0x51/0x100  <c022b817> tcp_sendmsg+0x897/0x980
>>>>  <c0153fa9> core_sys_select+0x1b9/0x2b0  <c0241f1d> inet_sendmsg+0x3d/0x50
>>>>  <c0202a8f> do_sock_write+0x8f/0xa0  <c020301f> sock_aio_write+0x5f/0x70
>>>>  <c01443d3> do_sync_write+0xc3/0x100  <c01247f0> autoremove_wake_function+0x0/0x40
>>>>  <c0144ca1> vfs_write+0xa1/0x140  <c01451d3> sys_write+0x43/0x70
>>>>  <c0102ae7> syscall_call+0x7/0xb
>>>>
>>>> Does it tell you anything already? Is there something I may instrument? What
>>>> could the driver do wrong to trigger such bug?
>>> Do you have CONFIG_NET_SCHED enabled?
>>>
> 
> Sorry, this was most probably false alarm for the official stack. The
> problem now appears to be related to a patch against d80211 that is only
> present in the rt2x00 CVS.

Well, I said "most probably"...

The actual problem was meanwhile identified: shorewall happened to
overwrite the queueing discipline of wmaster0 with pfifo_fast. I found
the magic knob to tell shorewall to no longer do this (at least until I
want to manage traffic control that way...), but I still wonder if it is
an acceptable situation. Currently, the user can intentionally or
accidentally screw up the stack this way.

Jan


PS: Tests performed on a 2.6.17 kernel, but I don't see a reason why
newer kernels should be immune.


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