From 76bc35e78fdf1065ffa2bb62fabe3e8423d378c8 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Mon, 11 Mar 2013 16:44:26 -0400 Subject: [PATCH] tty: Fix ldisc halt sequence on hangup Flip buffer work cannot be cancelled until all outstanding ldisc references have been released. Convert the ldisc ref wait into a full ldisc halt with buffer work cancellation. Note that the legacy mutex is not held while cancelling. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_ldisc.c | 39 +++++++++++++++++++-------------------- 1 file changed, 19 insertions(+), 20 deletions(-) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index fa0170e1b082..15667c0fd645 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -551,22 +551,30 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout) } /** - * tty_ldisc_hangup_wait_idle - wait for the ldisc to become idle - * @tty: tty to wait for - * - * Wait for the line discipline to become idle. The discipline must - * have been halted for this to guarantee it remains idle. + * tty_ldisc_hangup_halt - halt the line discipline for hangup + * @tty: tty being hung up * + * Shut down the line discipline and work queue for the tty device + * being hungup. Clear the TTY_LDISC flag to ensure no further + * references can be obtained, wait for remaining references to be + * released, and cancel pending buffer work to ensure no more + * data is fed to this ldisc. * Caller must hold legacy and ->ldisc_mutex. * * NB: tty_set_ldisc() is prevented from changing the ldisc concurrently * with this function by checking the TTY_HUPPING flag. + * + * NB: if tty->ldisc is NULL then buffer work does not need to be + * cancelled because it must already have done as a precondition + * of closing the ldisc and setting tty->ldisc to NULL */ -static bool tty_ldisc_hangup_wait_idle(struct tty_struct *tty) +static bool tty_ldisc_hangup_halt(struct tty_struct *tty) { char cur_n[TASK_COMM_LEN], tty_n[64]; long timeout = 3 * HZ; + clear_bit(TTY_LDISC, &tty->flags); + if (tty->ldisc) { /* Not yet closed */ tty_unlock(tty); @@ -577,6 +585,10 @@ static bool tty_ldisc_hangup_wait_idle(struct tty_struct *tty) __func__, get_task_comm(cur_n, current), tty_name(tty, tty_n)); } + + cancel_work_sync(&tty->port->buf.work); + set_bit(TTY_LDISC_HALTED, &tty->flags); + /* must reacquire both locks and preserve lock order */ mutex_unlock(&tty->ldisc_mutex); tty_lock(tty); @@ -851,24 +863,11 @@ void tty_ldisc_hangup(struct tty_struct *tty) */ mutex_lock(&tty->ldisc_mutex); - /* - * this is like tty_ldisc_halt, but we need to give up - * the BTM before calling cancel_work_sync, which may - * need to wait for another function taking the BTM - */ - clear_bit(TTY_LDISC, &tty->flags); - tty_unlock(tty); - cancel_work_sync(&tty->port->buf.work); - set_bit(TTY_LDISC_HALTED, &tty->flags); - mutex_unlock(&tty->ldisc_mutex); - tty_lock(tty); - mutex_lock(&tty->ldisc_mutex); - /* At this point we have a closed ldisc and we want to reopen it. We could defer this to the next open but it means auditing a lot of other paths so this is a FIXME */ - if (tty_ldisc_hangup_wait_idle(tty)) { + if (tty_ldisc_hangup_halt(tty)) { if (reset == 0) { if (!tty_ldisc_reinit(tty, tty->termios.c_line)) -- 2.30.2