linux-kernel - Re: tty: ctrl-c not always echoed, especially under load

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Message-ID: <20080805001129.72d06e60@lxorguk.ukuu.org.uk>
Date:	Tue, 5 Aug 2008 00:11:29 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Joe Peterson <joe@...rush.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: tty: ctrl-c not always echoed, especially under load

On Mon, 04 Aug 2008 16:03:02 -0600
Joe Peterson <joe@...rush.com> wrote:

> I am experiencing a rather intermittent and hard-to-reproduce issue in the tty
> layer, and I am posting here to get ideas on how to debug it from those of you
> who have delved into the tty internals.  I suspect some kind of race is going on
> or the echo is caught in the tty buffer when it gets flushed (and never makes it
> to the tty).  Heavy load (compiling, etc.) seems to make it more likely.
> 
> When a signal character (e.g. ctrl-c) is received, the tty ldisc and driver are
> flushed, the character is echoed (e.g. "^C" if echoctl is on), and the signal is
> issued.  Because the flush happens first, the echo should always appear on the
> tty, but sometimes it does not.  What I am wondering is how the echo could get
> "swallowed".  The code I have been using to test this is:

If the output buffer is full then echoed characters/^C etc will vanish the
way n_tty implements its buffering internally. It's always worked that
way.

Alan
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