linux-kernel - Re: [Bug #14388] keyboard under X with 2.6.31

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Date:	Tue, 13 Oct 2009 21:55:25 -0300 (BRST)
From:	"Frédéric L. W. Meunier" 
	<fredlwm@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Boyan <btanastasov@...oo.co.uk>,
	"Justin P. Mattock" <justinmattock@...il.com>,
	Nix <nix@...eri.org.uk>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Paul Fulghum <paulkf@...rogate.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Ed Tomlinson <edt@....ca>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [Bug #14388] keyboard under X with 2.6.31

On Tue, 13 Oct 2009, Linus Torvalds wrote:

>
> Another bug:
>
> On Tue, 13 Oct 2009, Linus Torvalds wrote:
>>  			if (!count) {
>> -				if (head->next == NULL)
>> -					break;
>
> Those two lines should _not_ be deleted. I cleaned up a bit too much.
>
> The rule is that we must not free the last buffer, because it's also going
> to be 'tail'.
>
> So here's a new version with that fixed (and the previous bug I already
> mentioned).
>
> Whether it _works_ is still not clear. It might eat your pet goldfish, or
> make farting noises in your general direction. Or it might fix the bug.
> Who knows?
>
> 		Linus
>
> ---
> drivers/char/tty_buffer.c |   29 +++++++++++++----------------
> 1 files changed, 13 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
> index 3108991..0296612 100644
> --- a/drivers/char/tty_buffer.c
> +++ b/drivers/char/tty_buffer.c
> @@ -402,28 +402,26 @@ static void flush_to_ldisc(struct work_struct *work)
> 		container_of(work, struct tty_struct, buf.work.work);
> 	unsigned long 	flags;
> 	struct tty_ldisc *disc;
> -	struct tty_buffer *tbuf, *head;
> -	char *char_buf;
> -	unsigned char *flag_buf;
>
> 	disc = tty_ldisc_ref(tty);
> 	if (disc == NULL)	/*  !TTY_LDISC */
> 		return;
>
> 	spin_lock_irqsave(&tty->buf.lock, flags);
> -	/* So we know a flush is running */
> -	set_bit(TTY_FLUSHING, &tty->flags);
> -	head = tty->buf.head;
> -	if (head != NULL) {
> -		tty->buf.head = NULL;
> -		for (;;) {
> -			int count = head->commit - head->read;
> +
> +	if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
> +		struct tty_buffer *head;
> +		while ((head = tty->buf.head) != NULL) {
> +			int count;
> +			char *char_buf;
> +			unsigned char *flag_buf;
> +
> +			count = head->commit - head->read;
> 			if (!count) {
> 				if (head->next == NULL)
> 					break;
> -				tbuf = head;
> -				head = head->next;
> -				tty_buffer_free(tty, tbuf);
> +				tty->buf.head = head->next;
> +				tty_buffer_free(tty, head);
> 				continue;
> 			}
> 			/* Ldisc or user is trying to flush the buffers
> @@ -445,9 +443,9 @@ static void flush_to_ldisc(struct work_struct *work)
> 							flag_buf, count);
> 			spin_lock_irqsave(&tty->buf.lock, flags);
> 		}
> -		/* Restore the queue head */
> -		tty->buf.head = head;
> +		clear_bit(TTY_FLUSHING, &tty->flags);
> 	}
> +
> 	/* We may have a deferred request to flush the input buffer,
> 	   if so pull the chain under the lock and empty the queue */
> 	if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
> @@ -455,7 +453,6 @@ static void flush_to_ldisc(struct work_struct *work)
> 		clear_bit(TTY_FLUSHPENDING, &tty->flags);
> 		wake_up(&tty->read_wait);
> 	}
> -	clear_bit(TTY_FLUSHING, &tty->flags);
> 	spin_unlock_irqrestore(&tty->buf.lock, flags);
>
> 	tty_ldisc_deref(disc);

For now (more than 3h), it isn't doing any harm. And no keyboard 
lockups.

BTW, the old version of the patch was funny. It booted, but at 
the login prompt I could only enter the first letter.
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