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From:   Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Date:   Thu, 21 Mar 2019 22:43:30 +0000
Message-ID: <CADVatmNVM3a=L6McdCsr5xzCwZnW6N4r9Cf55gjQZjsGGosBDg@mail.gmail.com>
Subject: Re: regression (bisected): "modprobe parport_pc" hangs in current mainline
To:     Michal Kubecek <mkubecek@suse.cz>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>
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HI Michal,

On Wed, Mar 20, 2019 at 9:18 PM Michal Kubecek <mkubecek@suse.cz> wrote:
>
> On Wed, Mar 20, 2019 at 09:30:59AM +0000, Sudip Mukherjee wrote:
> > Sorry, I didn't get the chance to look at it yet and have kept it
> > pending for this weekend. But just had a quick look and I was
> > wondering if the machine on which you are trying the modprobe has an
> > actual parallel port or the machine is not having any parallel port.
> > And also will you be able to send me a dmesg please.
>
> Attaching dmesg output from a virtual machine which doesn't seem to have
> a (virtual) parallel port. This part:
>
> [   63.962283] parport_pc 00:05: reported by Plug and Play ACPI
> [   63.962469] parport0: PC-style at 0x378, irq 7 [PCSPP,TRISTATE]
> [   64.061723] ppdev: user-space parallel port driver
>
> was after I manually killed "/sbin/modprobe -q -- parport_lowlevel" which
> was started during boot.

Thanks for testing. I am unable to reproduce the problem in VM or in
machine, with or without parallel port. But from your logs it looks
like you have an alias set for "parport_lowlevel". When parport module
is being loaded if it does not find any port in its list, it will try
to load "parport_lowlevel" and that is where you are getting the
deadlock. "parport_lowlevel" is not a real module, but instead should
be an alias pointing to some real module. I tried by setting an alias
of parport_lowlevel" as parport_pc but still could not get the
problem.
Can you please check in your VM or machine what do you have the alias
as? It should be either in "/etc/modprobe.conf" or some conf file in
"/etc/modprobe.d" folder. And also, will you be able to test a debug
patch on your VM?

-- 
Regards
Sudip