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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.


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:<>)
- 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
- lock ldisc without (5*HZ) timeout in tty_reopen()

v1 link:<>
v2 link:<>
v3 link:<>
v4 link:<>

Cc: Daniel Axtens <>
Cc: Dmitry Vyukov <>
Cc: Mark Rutland <>
Cc: Michael Neuling <>
Cc: Mikulas Patocka <>
Cc: Nathan March <>
Cc: Pasi Kärkkäinen <>
Cc: Peter Hurley <>
Cc: Peter Zijlstra <>
Cc: "Rong, Chen" <>
Cc: Sergey Senozhatsky <>
Cc: Tan Xiaojun <>
Cc: Tetsuo Handa <>
(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(-)


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