tty: Replace ldisc locking with ldisc_sem
Line discipline locking was performed with a combination of
a mutex, a status bit, a count, and a waitqueue -- basically,
a rw semaphore.
Replace the existing combination with an ld_semaphore.
Fixes:
1) the 'reference acquire after ldisc locked' bug
2) the over-complicated halt mechanism
3) lock order wrt. tty_lock()
4) dropping locks while changing ldisc
5) previously unidentified deadlock while locking ldisc from
both linked ttys concurrently
6) previously unidentified recursive deadlocks
Adds much-needed lockdep diagnostics.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index fa80af3..0fa5db4 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1388,8 +1388,7 @@
struct tty_driver *driver = tty->driver;
if (test_bit(TTY_CLOSING, &tty->flags) ||
- test_bit(TTY_HUPPING, &tty->flags) ||
- test_bit(TTY_LDISC_CHANGING, &tty->flags))
+ test_bit(TTY_HUPPING, &tty->flags))
return -EIO;
if (driver->type == TTY_DRIVER_TYPE_PTY &&
@@ -1405,7 +1404,7 @@
}
tty->count++;
- WARN_ON(!test_bit(TTY_LDISC, &tty->flags));
+ WARN_ON(!tty->ldisc);
return 0;
}
@@ -3017,7 +3016,7 @@
tty->pgrp = NULL;
mutex_init(&tty->legacy_mutex);
mutex_init(&tty->termios_mutex);
- mutex_init(&tty->ldisc_mutex);
+ init_ldsem(&tty->ldisc_sem);
init_waitqueue_head(&tty->write_wait);
init_waitqueue_head(&tty->read_wait);
INIT_WORK(&tty->hangup_work, do_tty_hangup);