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

[Boyan]

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);


It works for me. I couldn't reproduce the problem with this patch on top
of 2.6.31.3 with CONFIG_PREEMPT=y.
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