linux-kernel - Re: [PATCH] vt: kill tty->count usage

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Date:	Fri, 8 Aug 2008 22:26:35 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Aristeu Rozanski <arozansk@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	jirislaby@...il.com
Subject: Re: [PATCH] vt: kill tty->count usage

> each driver can keep the number of the references itself. Holding tty_mutex
> before calling driver's close() and updating tty->count is not possible
> because some drivers sleep waiting until the tx buffer is empty.

Agreed.

> This patch was tested under normal usage and using the stress application I
> wrote that triggers the problem more easily.
>
> +			if (vc->vc_tty != NULL) {
> +				/* we're still releasing this console entry */
> +				release_console_sem();
> +				return -EBUSY;

That isn't valid behaviour according to the POSIX tty rules. An open of a
closing tty blocks until the close completes. Most drivers using the
TTY_CLOSING flag to handle this.

So NAK the patch but basically agree with the approach - the EBUSY needs
to become a 'wait for close to complete, goto retry'

Alan

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