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    SubjectRe: [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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