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

Boyan
2009-10-14T07:45:31Z

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.