[PATCH 0/4] tty: Hold write ldisc sem in tty_reopen()

[Dmitry Safonov <dima@arista.com>]

Two fixes for potential and real issues.
Looks worth to have in stables as we've hit it on v4.9 stable.
And for linux-next - adding lockdep asserts for line discipline changing
code, verifying that write ldisc sem will be held forthwith.

I couldn't verify that holding write lock fixes the issue as we've hit
it only once and I've failed in reproducing it.
But searching in lkml, Cc'ing here people who probably had the same
crash (and in hope someone of them could give tested-by):

Cc: Daniel Axtens <dja@axtens.net> 
Cc: Dmitry Vyukov <dvyukov@google.com> 
Cc: Michael Neuling <mikey@neuling.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Pasi Kärkkäinen <pasik@iki.fi>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> 
Cc: Tan Xiaojun <tanxiaojun@huawei.com>
(please, ignore if I Cc'ed you mistakenly)

Dmitry Safonov (4):
  tty: Drop tty->count on tty_reopen() failure
  tty: Hold tty_ldisc_lock() during tty_reopen()
  tty: Lock tty pair in tty_init_dev()
  tty/lockdep: Add ldisc_sem asserts

 drivers/tty/tty_io.c    | 21 +++++++++++++++------
 drivers/tty/tty_ldisc.c | 12 ++++++++----
 include/linux/tty.h     |  4 ++++
 3 files changed, 27 insertions(+), 10 deletions(-)

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2.13.6