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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
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4
include/linux/tty.h
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@ -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 */