linux-kernel - Force mkiss to reset the line discipline when serial device is removed

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Date:	Thu, 01 Oct 2015 18:56:39 +0200
From:	Jean-Christian de Rivaz <jc@...is.ch>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>
Cc:	Thomas Osterried <thomas@...erried.de>,
	David Ranch <dranch@...nnet.net>,
	Ralf Baechle DL5RB <ralf@...ux-mips.org>,
	linux-hams@...nnet.net, linux-hams@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Force mkiss to reset the line discipline when serial device is removed

Hi Greg and Jiri,

I try to fix a kernel panic bug related to the AX25 (and probably SLIP) 
line discipline when the corresponding serial device is removed [1]. I 
proposed some patches [2] [3] on the linux-hams mailing list but I think 
there raise more questions about how tty_ldisc_hangup() should work when 
a serial device is removed [4].

I actually see the following options:

a) Let the specific line discipline set the TTY_DRIVER_RESET_TERMIOS 
flag in tty->driver as in [2] but this is suspected bad practice [5].

b) Let the specific line discipline set the TTY_OTHER_CLOSED flag in tty 
and check it in tty_ldisc_hangup() as in [3].

c) Let the specific line discipline set the TTY_LDISC_HALTED flag in tty 
and check it in tty_ldisc_hangup().

d) Let the specific line discipline set a new flag for that purpose, for 
example TTY_LDISC_RESET, and check it in tty_ldisc_hangup().

e) Close the tty earlier so that tty_ldisc_reinit() is not even called. 
Need some advise on how this should be done.

f) That's all wrong, something other need to be changed.

I would appreciate some comments from tty subsystem experts about this 
issue.

[1] http://www.spinics.net/lists/linux-hams/msg03500.html
[2] http://www.spinics.net/lists/linux-hams/msg03511.html
[3] http://www.spinics.net/lists/linux-hams/msg03513.html
[4] http://www.spinics.net/lists/linux-hams/msg03509.html
[5] http://www.spinics.net/lists/linux-hams/msg03512.html

Best Regards,
Jean-Christian de Rivaz

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