linux-kernel - Re: Soft lockup in rt2x00usb_work

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Date:   Wed, 08 Nov 2017 12:07:15 +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()

Le mercredi 08 novembre 2017 à 11:37 +0100, Stanislaw Gruszka a écrit :
> On Tue, Nov 07, 2017 at 12:01:23PM +0100, Richard Genoud wrote:
> > Le mardi 07 novembre 2017 à 11:13 +0100, Stanislaw Gruszka a
> > écrit :
> > > On Tue, Nov 07, 2017 at 11:06:39AM +0100, Richard Genoud wrote:
> > > > > 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 :)
> > > 
> > > You should configure function trace with rt2x* functions. After
> > > that
> > > start tracing, unbind the device, then stop tracing and provide
> > > trace
> > > output.
> > 
> > Ok, I found a way to display the trace (after the unbind, the board
> > is
> > frozen and I can't type anything).
> > Adding
> > CONFIG_SOFTLOCKUP_DETECTOR=y
> > CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC=y
> > along with echo 1 > /proc/sys/kernel/ftrace_dump_on_oops does the
> > trick
> 
> No, that not I wanted you to do. Please remove those options and just
> do
> below on tracing directory.
> 
> echo 0 > tracing_on 
> cat trace >  /dev/null
> echo "function_graph" > current_tracer 
> echo "rt2*" > set_ftrace_filter 
> echo 1 > tracing_on
> echo 1-2.2 > /sys/bus/usb/drivers/usb/unbind
> echo 0 > tracing_on
> cat trace > ~/trace.txt

Well, there's clearly a misunderstanding here :
After the command "echo 1-2.2 > /sys/bus/usb/drivers/usb/unbind"
I can't type *anything*
The only thing I can do is plug off the board.
This command never returns, so I can't stop the tracing...

Or I missed something ?

(maybe if there was more than one CPU on the board, I could do
something, but that's not the case)

> 
> and provide trace.txt to me (can be in private email if big).
> 
> Thanks
> Stanislaw

Thanks,
Richard.