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

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Date:   Thu, 3 Jan 2019 07:57:00 -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 3, 2019, at 3:32 AM, Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> wrote:
> 
> On 2019/01/03 18:09, Jiri Slaby wrote:
>> On 02. 01. 19, 16:04, Tetsuo Handa wrote:
>>> +	if (wait_event_interruptible(tty->read_wait,
>>> +	     (ret = -EIO, test_bit(TTY_OTHER_CLOSED, &tty->flags)) ||
>>> +	     (ret = 0, tty_hung_up_p(file)) ||
>>> +	     (rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)) != NULL ||
>>> +	     (ret = -EAGAIN, tty_io_nonblock(tty, file))))
>>> +		return -EINTR;
>> 
>> Oh, that looks really ugly. Could you move all this to a function
>> returning a bool and taking &ret and &rbuf as parameters?
>> 
> 
> OK. Something like this?

I agree with Jiri that placing all the conditional logic in a single expression is difficult to read.

But exchanging that many locals with a separate function defeats the original purpose of
simplifying code and this implementation changes the logic (write no
longer checks for line discipline changing under it during wait).

Converting to wait_event_interruptible where possible is a good goal but this instance
may be better left alone. The current structure mirrors the existing n_tty line discipline.