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tty: Remove unnecessary re-test of ldisc ref count 

Since the tty->ldisc is prevented from being changed by tty_set_ldisc()
when a tty is being hung up, re-testing the ldisc user count is
unnecessary -- ie, it cannot be a different ldisc and the user count
cannot have increased (assuming the caller meets the precondition that
TTY_LDISC flag is cleared)

Removal of the 'early-out' locking optimization is necessary for
the subsequent patch 'tty: Fix ldisc halt sequence on hangup'.

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 16:44:25 -04:00 committed by Greg Kroah-Hartman
parent 168942c9fa
commit 2276ad9765
1 changed files with 18 additions and 18 deletions
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36
drivers/tty/tty_ldisc.c
View File

@ -558,29 +558,29 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
* have been halted for this to guarantee it remains idle. * have been halted for this to guarantee it remains idle.
* *
* Caller must hold legacy and ->ldisc_mutex. * 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.
*/ */
static bool tty_ldisc_hangup_wait_idle(struct tty_struct *tty) static bool tty_ldisc_hangup_wait_idle(struct tty_struct *tty)
{ {
while (tty->ldisc) { /* Not yet closed */ char cur_n[TASK_COMM_LEN], tty_n[64];
if (atomic_read(&tty->ldisc->users) != 1) { long timeout = 3 * HZ;
char cur_n[TASK_COMM_LEN], tty_n[64];
long timeout = 3 * HZ;
tty_unlock(tty);
while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) { if (tty->ldisc) { /* Not yet closed */
timeout = MAX_SCHEDULE_TIMEOUT; tty_unlock(tty);
printk_ratelimited(KERN_WARNING
"%s: waiting (%s) for %s took too long, but we keep waiting...\n", while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
__func__, get_task_comm(cur_n, current), timeout = MAX_SCHEDULE_TIMEOUT;
tty_name(tty, tty_n)); printk_ratelimited(KERN_WARNING
} "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
/* must reacquire both locks and preserve lock order */ __func__, get_task_comm(cur_n, current),
mutex_unlock(&tty->ldisc_mutex); tty_name(tty, tty_n));
tty_lock(tty);
mutex_lock(&tty->ldisc_mutex);
continue;
} }
break; /* must reacquire both locks and preserve lock order */
mutex_unlock(&tty->ldisc_mutex);
tty_lock(tty);
mutex_lock(&tty->ldisc_mutex);
} }
return !!tty->ldisc; return !!tty->ldisc;
} }