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Date: Mon, 02 Jul 2012 10:21:21 -0500
From: Larry Finger <Larry.Finger@lwfinger.net>
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To: Johannes Berg <johannes@sipsolutions.net>
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Subject: Kernel oops in __netif_schedule() for at76c50x-usb
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Regarding the oops that I reported for PPC architecture that reported "Unable to 
handle kernel paging request for data at address 0x000004c", I have now repeated 
it on x86_64 architecture, where the objdump tool is better. The error occurs in 
the line in __netif_schedule() that says

          if (!test_and_set_bit(__QDISC_STATE_SCHED, &q->state))

Debug printouts have shown that q is not NULL, and it appears to be in the 
correct address range. I think q->state is zero; however, q->state cannot be 
written.

Additional testing shows this problem to be another side effect of commit 
3a25a8c ("mac80211: add improved HW queue control") for a device with only a 
single HW queue.

Any suggestions for additional debugging printouts will be greatly appreciated.

Thanks,

Larry