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tty: Don't hold ldisc lock in tty_reopen() if ldisc present

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Try to get reference for ldisc during tty_reopen().
If ldisc present, we don't need to do tty_ldisc_reinit() and lock the
write side for line discipline semaphore.
Effectively, it optimizes fast-path for tty_reopen(), but more
importantly it won't interrupt ongoing IO on the tty as no ldisc change
is needed.
Fixes user-visible issue when tty_reopen() interrupted login process for
user with a long password, observed and reported by Lukas.

Fixes: c96cf923a9 ("tty: Don't block on IO when ldisc change is pending")
Fixes: 83d817f410 ("tty: Hold tty_ldisc_lock() during tty_reopen()")
Cc: Jiri Slaby <[email protected]>
Reported-by: Lukas F. Hartmann <[email protected]>
Tested-by: Lukas F. Hartmann <[email protected]>
Cc: stable <[email protected]>
Signed-off-by: Dmitry Safonov <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Dmitry Safonov 2019-01-09 01:17:40 +00:00 • committed by Greg Kroah-Hartman
commit d3736d82e8
1 changed files with 13 additions and 7 deletions
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20
drivers/tty/tty_io.c
View file

@ -1256,7 +1256,8 @@ static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *
static int tty_reopen(struct tty_struct *tty)
{
struct tty_driver *driver = tty->driver;
int retval;
struct tty_ldisc *ld;
int retval = 0;
if (driver->type == TTY_DRIVER_TYPE_PTY &&
driver->subtype == PTY_TYPE_MASTER)
@ -1268,13 +1269,18 @@ static int tty_reopen(struct tty_struct *tty)
if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
return -EBUSY;
retval = tty_ldisc_lock(tty, 5 * HZ);
if (retval)
return retval;
ld = tty_ldisc_ref_wait(tty);
if (ld) {
tty_ldisc_deref(ld);
} else {
retval = tty_ldisc_lock(tty, 5 * HZ);
if (retval)
return retval;
if (!tty->ldisc)
retval = tty_ldisc_reinit(tty, tty->termios.c_line);
tty_ldisc_unlock(tty);
if (!tty->ldisc)
retval = tty_ldisc_reinit(tty, tty->termios.c_line);
tty_ldisc_unlock(tty);
}
if (retval == 0)
tty->count++;