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

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Message-ID: <877ic5irsu.fsf@denkblock.local>
Date:	Tue, 01 Jul 2008 16:48:33 +0200
From:	Elias Oltmanns <eo@...ensachen.de>
To:	Joe Peterson <joe@...rush.com>
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

Joe Peterson <joe@...rush.com> wrote:
> 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.

Due to my tests, 2.6.24 responds much faster to Ctrl+C than 2.6.25 does.
The patch above makes them *feel* alike again (no hard numbers, mind).
However, I haven't checked anything as early as 2.6.21 or before so I
don't know whether there may have been another regression since then.

Regards,

Elias
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