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tty: Fix hung task on pty hangup 

When hanging up one end of a pty pair, there may be waiting
readers/writers on the other end which may not exit, preventing
tty_ldisc_lock_pair() from acquiring the other side's ldisc lock.

Only acquire this side's ldisc lock; although this will no longer
prevent the other side from writing new input, that input will not
be processing until after the ldisc hangup is complete.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2014-11-05 12:13:07 -05:00 committed by Greg Kroah-Hartman
parent e80a10ee4d
commit fae76e9adf
1 changed files with 20 additions and 2 deletions
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22
drivers/tty/tty_ldisc.c
View File

@ -325,6 +325,24 @@ static inline void __tty_ldisc_unlock(struct tty_struct *tty)
return ldsem_up_write(&tty->ldisc_sem); return ldsem_up_write(&tty->ldisc_sem);
} }
static int __lockfunc
tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
{
int ret;
ret = __tty_ldisc_lock(tty, timeout);
if (!ret)
return -EBUSY;
set_bit(TTY_LDISC_HALTED, &tty->flags);
return 0;
}
static void tty_ldisc_unlock(struct tty_struct *tty)
{
clear_bit(TTY_LDISC_HALTED, &tty->flags);
__tty_ldisc_unlock(tty);
}
static int __lockfunc static int __lockfunc
tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2, tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
unsigned long timeout) unsigned long timeout)
@ -682,7 +700,7 @@ void tty_ldisc_hangup(struct tty_struct *tty)
* *
* Avoid racing set_ldisc or tty_ldisc_release * Avoid racing set_ldisc or tty_ldisc_release
*/ */
tty_ldisc_lock_pair(tty, tty->link); tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
if (tty->ldisc) { if (tty->ldisc) {
@ -704,7 +722,7 @@ void tty_ldisc_hangup(struct tty_struct *tty)
WARN_ON(tty_ldisc_open(tty, tty->ldisc)); WARN_ON(tty_ldisc_open(tty, tty->ldisc));
} }
} }
tty_ldisc_enable_pair(tty, tty->link); tty_ldisc_unlock(tty);
if (reset) if (reset)
tty_reset_termios(tty); tty_reset_termios(tty);