linux-kernel - RE: Re: Re: Re: Re: [syzbot] INFO: rcu detected stall in tx

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Date:   Thu, 6 May 2021 20:31:07 +0000
From:   Guido Kiener <Guido.Kiener@...de-schwarz.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+e2eae5639e7203360018@...kaller.appspotmail.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "dpenkler@...il.com" <dpenkler@...il.com>,
        "lee.jones@...aro.org" <lee.jones@...aro.org>,
        USB list <linux-usb@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "dwmw@...zon.co.uk" <dwmw@...zon.co.uk>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>
Subject: RE: Re: Re: Re: Re: [syzbot] INFO: rcu detected stall in tx

> -----Original Message-----
> From: Alan Stern
> Sent: Thursday, May 6, 2021 8:32 PM
> To: Kiener Guido 14DS1
> 
> On Thu, May 06, 2021 at 05:44:55PM +0000, Guido Kiener wrote:
> > > -----Original Message-----
> > > From: Alan Stern
> > > Sent: Thursday, May 6, 2021 3:49 PM
> > > To: Kiener Guido 14DS1 <Guido.Kiener@...de-schwarz.com>
> > > >
> > > > Thanks for your assessment. I agree with the general feeling. I
> > > > counted about hundred specific usb drivers, so wouldn't it be
> > > > better to fix the
> > > problem in some of the host drivers (e.g. urb.c)?
> > > > We could return an error when calling usb_submit_urb() on an erroneous
> pipe.
> > > > I cannot estimate the side effects and we need to check all
> > > > drivers again how they deal with the error situation. Maybe there
> > > > are some special driver
> > > that need a specialized error handling.
> > > > In this case these drivers could reset the (new?) error flag to
> > > > allow calling usb_submit_urb() again without error. This could work, isn't it?
> > >
> > > That is feasible, although it would be an awkward approach.  As you
> > > said, the side effects aren't clear.  But it might work.
> >
> > Otherwise I see only the other approach to change hundred drivers and
> > add the cases EPROTO, EILSEQ and ETIME in each callback handler. The
> > usbtmc driver already respects the EILSEQ and ETIME, and only EPROTO is
> missing.
> > The rest should be more a management task.
> > BTW do you assume it is only a problem for INT pipes or is it also a
> > problem for isochronous and bulk transfers?
> 
> All of them.  Control too.
> 
> > > Will you be able to test patches?
> >
> > I only can test the USBTMC function in some different PCs. I do not
> > have automated regression tests for USB drivers or Linux kernels.
> > Maybe there is company who could do that.
> 
> Well then, if I do find time to write a patch, I'll ask you to try it out with the usbtmc
> driver.

You mean that you will do a patch in urb.c or a host driver? Or just add a line in usbtmc.c?
Anyhow there is no hurry. On May 20 I will send you a mail if I'm able to
provoke one of these hardware errors EPROTO, EILSQ, or ETIME. Otherwise
it doesn't make sense to test it.

-Guido