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tty: Invert tty_lock/ldisc_sem lock order

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Dropping the tty lock to acquire the tty->ldisc_sem allows several
race conditions (such as hangup while changing the ldisc) which requires
extra states and testing. The ldisc_sem->tty_lock lock order has
not been required since tty buffer ownership was moved to tty_port.

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 12:12:45 -05:00 committed by Greg Kroah-Hartman
parent 3ee175d9d9
commit c8483bc9de
1 changed files with 3 additions and 4 deletions
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7
drivers/tty/tty_ldisc.c
View file

@ -523,9 +523,11 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
if (IS_ERR(new_ldisc))
return PTR_ERR(new_ldisc);
tty_lock(tty);
retval = tty_ldisc_lock_pair_timeout(tty, o_tty, 5 * HZ);
if (retval) {
tty_ldisc_put(new_ldisc);
tty_unlock(tty);
return retval;
}
@ -536,11 +538,11 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
if (tty->ldisc->ops->num == ldisc) {
tty_ldisc_enable_pair(tty, o_tty);
tty_ldisc_put(new_ldisc);
tty_unlock(tty);
return 0;
}
old_ldisc = tty->ldisc;
tty_lock(tty);
if (test_bit(TTY_HUPPING, &tty->flags) ||
test_bit(TTY_HUPPED, &tty->flags)) {
@ -675,8 +677,6 @@ void tty_ldisc_hangup(struct tty_struct *tty)
wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
wake_up_interruptible_poll(&tty->read_wait, POLLIN);
tty_unlock(tty);
/*
* Shutdown the current line discipline, and reset it to
* N_TTY if need be.
@ -684,7 +684,6 @@ void tty_ldisc_hangup(struct tty_struct *tty)
* Avoid racing set_ldisc or tty_ldisc_release
*/
tty_ldisc_lock_pair(tty, tty->link);
tty_lock(tty);
if (tty->ldisc) {