diff options
| author | Peter Hurley <peter@hurleysoftware.com> | 2013-03-11 21:44:41 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-03-19 00:48:42 +0100 |
| commit | 16759f6cd8c590fa23cb2956fdf32fe23a67e482 (patch) | |
| tree | cfd1c8eb346d6cae8bf82cc2211b21f79b449671 /drivers/tty/tty_ldisc.c | |
| parent | tty: Separate release semantics of ldisc reference (diff) | |
| download | linux-16759f6cd8c590fa23cb2956fdf32fe23a67e482.tar.xz linux-16759f6cd8c590fa23cb2956fdf32fe23a67e482.zip | |
tty: Document unsafe ldisc reference acquire
Merge get_ldisc() into its only call site.
Note how, after merging, the unsafe acquire of an ldisc reference
is obvious.
CPU 0 in tty_ldisc_try() | CPU 1 in tty_ldisc_halt()
|
test_bit(TTY_LDISC, &tty_flags) |
if (true) | clear_bit(TTY_LDISC, &tty_flags)
tty->ldisc != 0? | atomic_read(&tty->ldisc->users)
if (true) | ret_val == 1?
atomic_inc(&tty->ldisc->users) | if (false)
| wait
|
<goes on assuming safe ldisc use> | <doesn't wait - proceeds w/ close>
|
The spin lock in tty_ldisc_try() does nothing wrt synchronizing
the ldisc halt since it's not acquired as part of halting.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/tty_ldisc.c')
| -rw-r--r-- | drivers/tty/tty_ldisc.c | 14 |
1 files changed, 5 insertions, 9 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 9362a1030c95..5ee0b2be7d72 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -42,13 +42,6 @@ static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait); /* Line disc dispatch table */ static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS]; -static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld) -{ - if (ld) - atomic_inc(&ld->users); - return ld; -} - /** * tty_register_ldisc - install a line discipline * @disc: ldisc number @@ -269,10 +262,13 @@ static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty) unsigned long flags; struct tty_ldisc *ld; + /* FIXME: this allows reference acquire after TTY_LDISC is cleared */ raw_spin_lock_irqsave(&tty_ldisc_lock, flags); ld = NULL; - if (test_bit(TTY_LDISC, &tty->flags)) - ld = get_ldisc(tty->ldisc); + if (test_bit(TTY_LDISC, &tty->flags) && tty->ldisc) { + ld = tty->ldisc; + atomic_inc(&ld->users); + } raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); return ld; } |