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List:       linux-kernel
Subject:    Re: [PATCH] tty: Fix WARNING in tty_set_termios
From:       shuah <shuah () kernel ! org>
Date:       2019-01-31 23:23:02
Message-ID: 2812690e-d9d6-9755-ecb1-045e2acb4323 () kernel ! org
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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

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