linux-kernel - Re: [PATCH] tty: Fix SIGTTOU not sent with tcflush()

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Message-ID: <20130926163633.GA22849@redhat.com>
Date:	Thu, 26 Sep 2013 18:36:33 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	codonell <codonell@...hat.com>, Eduard Benes <ebenes@...hat.com>,
	Karel Srot <ksrot@...hat.com>,
	Matt Newsome <mnewsome@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] tty: Fix SIGTTOU not sent with tcflush()

Thanks Peter.

Well. I'am afraid my testing was wrong, because Karel reports
it fixes the problem...

But. I applied this patch to my 3.11 tree (last commit is bff157b3a)
which also has the additional patch (03e12617 "tty: disassociate_ctty()
sends the extra SIGCONT"), and

	TET_CONFIG=CFG TET_ROOT=.  ./T.tcflush 4

still fails... T.tcflush was compiled on another (Karel's) machine,
perhaps there is something in libc, I do not know.

So let me ask just in case, I assume the fix below doesn't depend on
other changes I could miss?

I'll retest after git-pull and report...

On 09/25, Peter Hurley wrote:
>
> Commit 'e7f3880cd9b98c5bf9391ae7acdec82b75403776'
>   tty: Fix recursive deadlock in tty_perform_flush()
> introduced a regression where tcflush() does not generate
> SIGTTOU for background process groups.
>
> Make sure ioctl(TCFLSH) calls tty_check_change() when
> invoked from the line discipline.
>
> Cc: stable@...r.kernel.org # v3.10+
> Reported-by: Oleg Nesterov <oleg@...hat.com>

Actually Reported-by: Karel Srot <ksrot@...hat.com>

my fault, forgot to mention this.

> Signed-off-by: Peter Hurley <peter@...leysoftware.com>
> ---
>  drivers/tty/tty_ioctl.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
> index 3500d41..088b4ca 100644
> --- a/drivers/tty/tty_ioctl.c
> +++ b/drivers/tty/tty_ioctl.c
> @@ -1201,6 +1201,9 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
>  		}
>  		return 0;
>  	case TCFLSH:
> +		retval = tty_check_change(tty);
> +		if (retval)
> +			return retval;
>  		return __tty_perform_flush(tty, arg);
>  	default:
>  		/* Try the mode commands */
> -- 
> 1.8.1.2
> 

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