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tty: Replace ldisc locking with ldisc_sem

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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
Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/tty/tty_buffer.c
View File

@@ -429,7 +429,7 @@ static void flush_to_ldisc(struct work_struct *work)
return;
disc = tty_ldisc_ref(tty);
if (disc == NULL) /* !TTY_LDISC */
if (disc == NULL)
return;
spin_lock_irqsave(&buf->lock, flags);

7
drivers/tty/tty_io.c
View File

@@ -1388,8 +1388,7 @@ static int tty_reopen(struct tty_struct *tty)
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 @@ static int tty_reopen(struct tty_struct *tty)
}
tty->count++;
WARN_ON(!test_bit(TTY_LDISC, &tty->flags));
WARN_ON(!tty->ldisc);
return 0;
}
@@ -3017,7 +3016,7 @@ void initialize_tty_struct(struct tty_struct *tty,
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);

329
drivers/tty/tty_ldisc.c
View File

File diff suppressed because it is too large Load Diff

4
include/linux/tty.h
View File

@@ -238,7 +238,7 @@ struct tty_struct {
int index;
/* Protects ldisc changes: Lock tty not pty */
struct mutex ldisc_mutex;
struct ld_semaphore ldisc_sem;
struct tty_ldisc *ldisc;
struct mutex atomic_write_lock;
@@ -305,8 +305,6 @@ struct tty_file_private {
#define TTY_DO_WRITE_WAKEUP 5 /* Call write_wakeup after queuing new */
#define TTY_PUSH 6 /* n_tty private */
#define TTY_CLOSING 7 /* ->close() in progress */
#define TTY_LDISC 9 /* Line discipline attached */
#define TTY_LDISC_CHANGING 10 /* Line discipline changing */
#define TTY_LDISC_OPEN 11 /* Line discipline is open */
#define TTY_PTY_LOCK 16 /* pty private */
#define TTY_NO_WRITE_SPLIT 17 /* Preserve write boundaries to driver */

3
include/linux/tty_ldisc.h
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