linux-kernel - Re: [PATCH 1/1] TTY: don't allow reopen when ldisc is changing

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Date:	Sat, 27 Nov 2010 10:43:54 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	unlisted-recipients:; (no To-header on input)
CC:	Kyle McMartin <kyle@...artin.ca>, gregkh@...e.de,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 1/1] TTY: don't allow reopen when ldisc is changing

On 11/27/2010 09:50 AM, Jiri Slaby wrote:
> On 11/27/2010 03:59 AM, Kyle McMartin wrote:
>> I'm poking around to see, I think maybe something might be dropping
>> locks in the callchain that gives us a window where this might be
>> possible...
> 
> Of course, that's the case:
>         clear_bit(TTY_LDISC, &tty->flags);
>         tty_unlock();
>         cancel_delayed_work_sync(&tty->buf.work);
>         mutex_unlock(&tty->ldisc_mutex);
> 
>         tty_lock();
>         mutex_lock(&tty->ldisc_mutex);
> 
> in tty_ldisc_hangup. Hence my point 1) from previous posts doesn't hold too:
> 1) __tty_hangup from tty_ldisc_hangup to tty_ldisc_enable. During this
> section tty_lock is held.
> 
> I will check, how to fix this.

Reproducible with 2 running processes from the attachment.

regards,
-- 
js
suse labs

View attachment "tty_reopen.c" of type "text/x-csrc" (1228 bytes)