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

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Date:   Mon, 19 Nov 2018 14:52:08 +0200
From:   Pasi Kärkkäinen <pasik@....fi>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        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>,
        Nathan March <nathan@...net>,
        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
Subject: Re: [PATCHv6 0/7] tty: Hold write ldisc sem in tty_reopen()

Hello Mikulas,

Any chance you could re-test these v6 patches? It seems you're able to relatively easily trigger the bug on your (pa-risc) environment.. I'd be good to have this series finally acked/merged!


Thanks a lot,

-- Pasi

On Thu, Nov 01, 2018 at 12:24:45AM +0000, Dmitry Safonov wrote:
> 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
>