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tty: Make lock subclasses available for other tty locks

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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: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2015-01-17 15:42:04 -05:00 • committed by Greg Kroah-Hartman
parent fb5ef9e7da
commit 3abf87cd3e
2 changed files with 18 additions and 11 deletions
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17
include/linux/tty.h
View file

@ -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