[PATCHv6 0/7] tty: Hold write ldisc sem in tty_reopen()

[Dmitry Safonov <dima@arista.com>]

Hi all,

Here are 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.

Mikulas, can you add your tested-by on this patches set again, please?
I tried to reproduce reboot issue on qemu-hppa and even built
cross-compiler for pa-risc.. but was unlucky in reproducing.

Thanks,
Dima

Changes since v5:
- Better commit tags
- Hopefully fixed issue with reboot on pa-risc with Debian 5

Changes since v4:
- back to lock ldisc with (5*HZ) timeout in tty_reopen()
  (LKP report link: lkml.kernel.org/r/<1536940609.3185.29.camel@arista.com>)
- reordered 3/7 with 2/7 for LKP robot

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>
v4 link: lkml.kernel.org/r/<20180912001702.18522-1-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/ldsem: Wake up readers after timed out down_write()
  tty: Hold tty_ldisc_lock() during tty_reopen()
  tty: Don't block on IO when ldisc change is pending
  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/n_hdlc.c    |  4 +--
 drivers/tty/n_r3964.c   |  2 +-
 drivers/tty/n_tty.c     |  8 +++---
 drivers/tty/tty_io.c    | 14 ++++++----
 drivers/tty/tty_ldisc.c | 16 +++++++++++
 drivers/tty/tty_ldsem.c | 62 +++++++++++++++++------------------------
 include/linux/tty.h     |  7 +++++
 7 files changed, 63 insertions(+), 50 deletions(-)

-- 
2.19.1