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Commit 3abf87cd authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
Browse files

tty: Make lock subclasses available for other tty locks 



Besides nested legacy_mutex locking which is required on pty pair
teardown, other nested pty operations require lock subclassing.

Move lock subclass definition to tty interface header, include/linux/tty.h,
and document its use.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fb5ef9e7

drivers/tty/tty_mutex.c

+1 −11
Original line number Diff line number Diff line
@@ -4,18 +4,8 @@ 
#include <linux/semaphore.h>

#include <linux/sched.h>



/*

 * Nested tty locks are necessary for releasing pty pairs.

 * The stable lock order is master pty first, then slave pty.

 */



/* Legacy tty mutex glue */



enum {

	TTY_MUTEX_NORMAL,

	TTY_MUTEX_SLAVE,

};



/*

 * Getting the big tty mutex.

 */
@@ -58,5 +48,5 @@ void __lockfunc tty_unlock_slave(struct tty_struct *tty) 


void tty_set_lock_subclass(struct tty_struct *tty)

{

	lockdep_set_subclass(&tty->legacy_mutex, TTY_MUTEX_SLAVE);

	lockdep_set_subclass(&tty->legacy_mutex, TTY_LOCK_SLAVE);

}

include/linux/tty.h

+17 −0
Original line number Diff line number Diff line
@@ -14,6 +14,23 @@ 
#include <linux/llist.h>





/*

 * Lock subclasses for tty locks

 *

 * TTY_LOCK_NORMAL is for normal ttys and master ptys.

 * TTY_LOCK_SLAVE is for slave ptys only.

 *

 * Lock subclasses are necessary for handling nested locking with pty pairs.

 * tty locks which use nested locking:

 *

 * legacy_mutex - Nested tty locks are necessary for releasing pty pairs.

 *		  The stable lock order is master pty first, then slave pty.

 */



enum {

	TTY_LOCK_NORMAL = 0,

	TTY_LOCK_SLAVE,

};



/*

 * (Note: the *_driver.minor_start values 1, 64, 128, 192 are