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>
This commit is contained in:
Peter Hurley 2013-06-15 07:04:48 -04:00 committed by Greg Kroah-Hartman
parent d2c438905f
commit 36697529b5
5 changed files with 52 additions and 293 deletions

View file

@ -203,8 +203,7 @@ struct tty_ldisc_ops {
struct tty_ldisc {
struct tty_ldisc_ops *ops;
atomic_t users;
wait_queue_head_t wq_idle;
struct tty_struct *tty;
};
#define TTY_LDISC_MAGIC 0x5403