linux-kernel - Re: patch "TTY: remove tty

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Message-ID: <2337681.paSeVyBarJ@wuerfel>
Date:	Tue, 23 Aug 2011 20:46:33 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	gregkh@...e.de, alan@...ux.intel.com,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: patch "TTY: remove tty_locked" added to tty tree

On Tuesday 23 August 2011 20:33:38 Jiri Slaby wrote:

> It looks like I need tty_locked to fix system stalls in
> tty_wait_until_sent in the end. Like with the patch attached. But if
> someone finds another way to fix this in short-term, it would be great.
>
> 
> @@ -153,8 +154,14 @@ void tty_wait_until_sent(struct tty_struct *tty, long timeout)
>  #endif
>  	if (!timeout)
>  		timeout = MAX_SCHEDULE_TIMEOUT;
> -	if (wait_event_interruptible_timeout(tty->write_wait,
> -			!tty_chars_in_buffer(tty), timeout) >= 0) {
> +
> +	if (tty_locked()) /* e.g. uart (holds) vs. tty_ioctl (does not) */
> +		retval = wait_event_interruptible_timeout_tty(tty->write_wait,
> +			!tty_chars_in_buffer(tty), timeout);
> +	else
> +		retval = wait_event_interruptible_timeout(tty->write_wait,
> +			!tty_chars_in_buffer(tty), timeout);
> 
> 

According to http://kernelnewbies.org/BigKernelLock, I concluded back then
that tty_wait_until_sent would always be called without BTM held. Has that
changed recently, or did I miss a caller that holds the BTM?

The only caller that used to call it with BKL was tty_set_ldisc, and that
got changed to release the BTM before calling it. If there is another
caller, can it do the same?

	Arnd
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