netdev - Re: [PATCH] tty: Fix WARNING in tty_set

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Date:   Thu, 31 Jan 2019 16:23:02 -0700
From:   shuah <shuah@...nel.org>
To:     Johan Hovold <johan@...nel.org>,
        Marcel Holtmann <marcel@...tmann.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        "open list:NFC SUBSYSTEM" <linux-wireless@...r.kernel.org>,
        chris@...-brannons.com, devel@...verdev.osuosl.org,
        Rob Herring <robh@...nel.org>,
        Samuel Ortiz <sameo@...ux.intel.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>, santhameena13@...il.com,
        kirk@...sers.ca, Johan Hedberg <johan.hedberg@...il.com>,
        Arnd Bergmann <arnd@...db.de>, samuel.thibault@...-lyon.org,
        m.maya.nakamura@...il.com, zhongjiang@...wei.com,
        Greg KH <gregkh@...uxfoundation.org>,
        speakup@...ux-speakup.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bluez mailing list <linux-bluetooth@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        nishka.dasgupta_ug18@...oka.edu.in,
        "David S. Miller" <davem@...emloft.net>, shuah <shuah@...nel.org>
Subject: Re: [PATCH] tty: Fix WARNING in tty_set_termios

On 1/31/19 8:33 AM, Johan Hovold wrote:
> On Thu, Jan 31, 2019 at 04:18:33PM +0100, Marcel Holtmann wrote:
> 
>>> I agree with Al that this change doesn't make much sense. The WARN_ON
>>> is there to catch any bugs leading to the termios being changed for a
>>> master side pty. Those should bugs should be fixed, and not worked
>>> around in order to silence a WARN_ON.
>>>
>>> The problem started with 7721383f4199 ("Bluetooth: hci_uart: Support
>>> operational speed during setup") which introduced a new way for how
>>> tty_set_termios() could end up being called for a master pty.
>>>
>>> As Al hinted at, setting these ldiscs for a master pty really makes no
>>> sense and perhaps that is what we should prevent unless simply making
>>> sure they do not call tty_set_termios() is sufficient for the time
>>> being.
>>>
>>> Finally, note that serdev never operates on a pty, and that this is only
>>> an issue for (the three) line disciplines.
>>
>> I think for PTYs we should just fail setting the HCI line discipline.
>> Fail early and just move on with life.
> 
> Sounds good to me. At least for the pty master. There may be some people
> trying to use a bluetooth device connected to a remote serial port (I've
> seen descriptions of such setups at least), and maybe we need not prevent
> that.
> 

Thanks for the feedback on the patch. Changes to prevent setting the HCI
line discipline from hci_uart fixes the problem.

I am sending v2 in a just a bit.

thanks,
-- Shuah