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tty: Fix ldisc halt sequence on hangup

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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 <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2013-03-11 16:44:26 -04:00 committed by Greg Kroah-Hartman
parent 2276ad9765
commit 76bc35e78f
1 changed files with 19 additions and 20 deletions
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39
drivers/tty/tty_ldisc.c
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@ -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))