[PATCHv3 0/6] tty: Hold write ldisc sem in tty_reopen()

From: Dmitry Safonov
Date: Mon Sep 10 2018 - 21:48:29 EST

Hi all,

Three fixes that worth to have in the @stable, as we've hit them on v4.9

And for linux-next - adding lockdep asserts for line discipline changing
code, verifying that write ldisc sem will be held forthwith.

The last patch is optional and probably, timeout can be dropped for
read_lock(). I'll do it if everyone agrees.

Rong Chen, could you kindly re-run this version to see if the lockup
from v1 still happens? I wasn't able to reproduce it..


Changes since v2:
- Added reviewed-by tags
- Hopefully, fixed reported by 0-day issue.
- Added optional fix for wait_readers decrement

Changes since v1:
- Added tested-by/reported-by tags
- Dropped 3/4 (locking tty pair for lockdep sake),
Because of that - not adding lockdep_assert_held() in tty_ldisc_open()
- Added 4/4 cleanup to inc tty->count only on success of
- lock ldisc without (5*HZ) timeout in tty_reopen()

v1 link:

Huuge cc list:
Cc: Daniel Axtens <dja@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Michael Neuling <mikey@xxxxxxxxxxx>
Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: Nathan March <nathan@xxxxxx>
Cc: Pasi KÃrkkÃinen <pasik@xxxxxx>
Cc: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Cc: "Rong, Chen" <rong.a.chen@xxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: Tan Xiaojun <tanxiaojun@xxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
(please, ignore if I Cc'ed you mistakenly)

Dmitry Safonov (6):
tty: Drop tty->count on tty_reopen() failure
tty/ldsem: Update waiter->task before waking up reader
tty: Hold tty_ldisc_lock() during tty_reopen()
tty/lockdep: Add ldisc_sem asserts
tty: Simplify tty->count math in tty_reopen()
tty/ldsem: Decrement wait_readers on timeouted down_read()

drivers/tty/tty_io.c | 12 ++++++++----
drivers/tty/tty_ldisc.c | 5 +++++
drivers/tty/tty_ldsem.c | 5 ++++-
3 files changed, 17 insertions(+), 5 deletions(-)