linux-kernel - Re: [PATCH] tty/n_hdlc: fix sleep in !TASK

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Date:   Fri, 4 Jan 2019 05:57:37 -0800
From:   Paul Fulghum <paulkf@...rogate.com>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     Jiri Slaby <jslaby@...e.cz>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Cox <alan@...rguk.ukuu.org.uk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

> On Jan 4, 2019, at 2:23 AM, Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:
> 
> But why not to clarify what are appropriate sanity checks?
> ...
> want a cleanup for scripts/checkpatch.pl .

These are good goals. I avoid purely cosmetic patches. I do not object to cosmetic patches from others that do not change behavior.

The checks that concern you deal with changing tty line disciplines. Dealing with line discipline changes has been an ongoing issue since n_hdlc was derived from other line disciplines 20 years ago, with major overhauls along the way. It is complex: driver layers shifting during operation while dealing properly with opens, closes, hangups, and sleeping operations. Patches have been added to the latest unreleased kernel to address line discipline changes, it is still evolving.

Why are the existing line discipline checks in n_hdlc where they are? Becasue that’s how they evolved from where they started to accomodate these changes. There are not many and their function is known: has the line discipline changed at that point? I know that is not satisfying but coming up with a definitive comment saying a check is absolutely required in one place and not in another requires more insight into the long history of a moving target than I have. Without that insight I would not alter existing checks in code that is not causing problems.