linux-kernel - Re: Soft lockup in rt2x00usb_work

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Date:   Tue, 7 Nov 2017 11:06:39 +0100
From:   Richard Genoud <richard.genoud@...il.com>
To:     Stanislaw Gruszka <sgruszka@...hat.com>
Cc:     Helmut Schaa <helmut.schaa@...glemail.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-wireless@...r.kernel.org
Subject: Re: Soft lockup in rt2x00usb_work_rxdone()

2017-11-07 9:53 GMT+01:00 Stanislaw Gruszka <sgruszka@...hat.com>:
> Hi
Hi !
>
> On Mon, Nov 06, 2017 at 04:57:09PM +0100, Richard Genoud wrote:
>> I get a soft lock-up while unbinding the USB driver on a TP-Link TL-WN727Nv3 (chipset 5370):
>>
>> # echo 1-2.2 > /sys/bus/usb/drivers/usb/unbind
>> watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [kworker/u2:3:308]
> ...
>> I can trigger this each time.
>
> I can not reproduce this on my system (I'm using 4.14.0-rc6, but I don't
> think it's an issue). I think the problem may be caused by usb
> host controler driver, which can be different on your system.
>
> Does ftrace work on your platform ? If so could you use ftrace
> to provide rt2x00 functions trace when the  probllem happen ?
>
> 3 short articles how to configure and use ftrace are here:
> https://lwn.net/Articles/365835/
> https://lwn.net/Articles/366796/
> https://lwn.net/Articles/370423/
>
I tried with ftrace, but I don't think there's a way to dump the trace
when there's a soft lock-up
(I can't do anything after the unbind, even the heartbeat led stopped blinking).
I saw the /proc/sys/kernel/ftrace_dump_on_oops file, but there's no
/proc/sys/kernel/ftrace_dump_on_soft_lock-up file :)

Or I missed something in ftrace ?

Thanks !
Richard.

> Thanks
> Stanislaw