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 <d...@axtens.net>
Cc: Dmitry Vyukov <dvyu...@google.com>
Cc: Michael Neuling <mi...@neuling.org>
Cc: Mikulas Patocka <mpato...@redhat.com>
Cc: Nathan March <nat...@gt.net>
Cc: Pasi Kärkkäinen <pa...@iki.fi>
Cc: Peter Hurley <pe...@hurleysoftware.com>
Cc: "Rong, Chen" <rong.a.c...@intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.w...@gmail.com>
Cc: Tan Xiaojun <tanxiao...@huawei.com>
Cc: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
(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(-)


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