linux-kernel - Re: Ctrl+C doesn't interrupt process waiting for I/O

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Message-ID: <486A3B4A.2090005@skyrush.com>
Date:	Tue, 01 Jul 2008 08:12:26 -0600
From:	Joe Peterson <joe@...rush.com>
To:	Elias Oltmanns <eo@...ensachen.de>
CC:	Török Edwin <edwintorok@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Ctrl+C doesn't interrupt process waiting for I/O



Elias Oltmanns wrote:
> The following patch to 2.6.26-rc8 fixes the issue for me. Perhaps we
> really want to do something else, but since I'm not all that familiar
> with the standard behaviour on other Unices and since the comment
> describing the changed order of function calls in the original commit
> didn't give the reason for that change, I leave that to more
> knowledgeable people.
> 
>  drivers/char/n_tty.c |   13 +------------
>  1 files changed, 1 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
> index 8096389..74018ef 100644
> --- a/drivers/char/n_tty.c
> +++ b/drivers/char/n_tty.c
> @@ -759,20 +759,9 @@ static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
>  		signal = SIGTSTP;
>  		if (c == SUSP_CHAR(tty)) {
>  send_signal:
> -			/*
> -			 * Echo character, and then send the signal.
> -			 * Note that we do not use isig() here because we want
> -			 * the order to be:
> -			 * 1) flush, 2) echo, 3) signal
> -			 */
> -			if (!L_NOFLSH(tty)) {
> -				n_tty_flush_buffer(tty);
> -				tty_driver_flush_buffer(tty);
> -			}
>  			if (L_ECHO(tty))
>  				echo_char(c, tty);
> -			if (tty->pgrp)
> -				kill_pgrp(tty->pgrp, signal, 1);
> +			isig(signal, tty, 0);
>  			return;
>  		}
>  	}

I noticed the original post in this thread mentioned that the problem
has been seen since 2.6.21 or 2.6.23:

> I use 2.6.25-2 and 2.6.26-rc8 now; I don't recall seeing this
> behaviour with old kernels (IIRC I see this since 2.6.21 or 2.6.23).
>
> Is this intended behaviour, or should I report a bug?

The echo patch that is altered in the patch above only appeared recently
(in 2.6.25).  Is there a way for you try try the test case on a
pre-2.6.25 kernel and see if the issue exists there?  If so, it is
strange that the above fixes it.

						-Joe
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