[PATCHv4 0/7] tty: Hold write ldisc sem in tty_reopen()

[Dmitry Safonov <dima@arista.com>]

Hi all,

Three fixes that worth to have in the @stable, as they were hit by
different people, including Arista 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.

The last patch is an optional and probably, timeout can be dropped for
read_lock(). I'll do it if everyone agrees.
(Or as per discussion with Peter in v3, just convert ldisc to
a regular rwsem).

Thanks,
Dima

Changes since v3:
- Added tested-by Mark Rutland (thanks!)
- Dropped patch with smp_wmb() - wrong idea
- lockdep_assert_held() should be actually lockdep_assert_held_exclusive()
- Described why tty_ldisc_open() can be called without ldisc_sem held
  for pty slave end (o_tty).
- Added Peter's patch for dropping self-made lockdep annotations
- Fix for a reader(s) of ldisc semaphore waiting for an active reader(s)

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
  tty_ldisc_reinit()
- lock ldisc without (5*HZ) timeout in tty_reopen()

v1 link: lkml.kernel.org/r/<20180829022353.23568-1-dima@arista.com>
v2 link: lkml.kernel.org/r/<20180903165257.29227-1-dima@arista.com>
v3 link: lkml.kernel.org/r/<20180911014821.26286-1-dima@arista.com>

Cc: Daniel Axtens <dja@axtens.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Nathan March <nathan@gt.net>
Cc: Pasi Kärkkäinen <pasik@iki.fi>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Rong, Chen" <rong.a.chen@intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Tan Xiaojun <tanxiaojun@huawei.com>
Cc: Tetsuo Handa <penguin-kernel@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: Hold tty_ldisc_lock() during tty_reopen()
  tty/ldsem: Wake up readers after timed out down_write()
  tty: Simplify tty->count math in tty_reopen()
  tty/ldsem: Add lockdep asserts for ldisc_sem
  tty/ldsem: Decrement wait_readers on timeouted down_read()

Peter Zijlstra (1):
  tty/ldsem: Convert to regular lockdep annotations

 drivers/tty/tty_io.c    | 12 ++++++----
 drivers/tty/tty_ldisc.c |  9 +++++++
 drivers/tty/tty_ldsem.c | 62 ++++++++++++++++++++-----------------------------
 3 files changed, 42 insertions(+), 41 deletions(-)

-- 
2.13.6