linux-kernel - [PATCHv6 0/7] tty: Hold write ldisc sem in tty

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Message-Id: <20181101002452.5483-1-dima@arista.com>
Date:   Thu,  1 Nov 2018 00:24:45 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        Daniel Axtens <dja@...ens.net>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Michael Neuling <mikey@...ling.org>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Nathan March <nathan@...net>,
        Pasi Kärkkäinen <pasik@....fi>,
        Peter Hurley <peter@...leysoftware.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rong, Chen" <rong.a.chen@...el.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tan Xiaojun <tanxiaojun@...wei.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, stable@...r.kernel.org,
        Jiri Slaby <jslaby@...e.cz>,
        syzbot+3aa9784721dfb90e984d@...kaller.appspotmail.com,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: [PATCHv6 0/7] tty: Hold write ldisc sem in tty_reopen()

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@...sta.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@...sta.com>
v2 link: lkml.kernel.org/r/<20180903165257.29227-1-dima@...sta.com>
v3 link: lkml.kernel.org/r/<20180911014821.26286-1-dima@...sta.com>
v4 link: lkml.kernel.org/r/<20180912001702.18522-1-dima@...sta.com>

Cc: Daniel Axtens <dja@...ens.net>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Michael Neuling <mikey@...ling.org>
Cc: Mikulas Patocka <mpatocka@...hat.com>
Cc: Nathan March <nathan@...net>
Cc: Pasi Kärkkäinen <pasik@....fi>
Cc: Peter Hurley <peter@...leysoftware.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: "Rong, Chen" <rong.a.chen@...el.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Tan Xiaojun <tanxiaojun@...wei.com>
Cc: Tetsuo Handa <penguin-kernel@...ove.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