linux-kernel - Re: [PATCHv5 0/7] tty: Hold write ldisc sem in tty

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Message-ID: <alpine.LRH.2.02.1809191330590.19146@file01.intranet.prod.int.rdu2.redhat.com>
Date:   Wed, 19 Sep 2018 13:35:16 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Dmitry Safonov <dima@...sta.com>
cc:     linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.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>,
        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>,
        stable@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Jiri Slaby <jslaby@...e.cz>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        syzbot+3aa9784721dfb90e984d@...kaller.appspotmail.com
Subject: Re: [PATCHv5 0/7] tty: Hold write ldisc sem in tty_reopen()



On Wed, 19 Sep 2018, Mikulas Patocka wrote:

> 
> 
> On Tue, 18 Sep 2018, Dmitry Safonov wrote:
> 
> > 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
> 
> I confirm that this patch series fixes the crash for me.
> 
> Tested-by: Mikulas Patocka <mpatocka@...hat.com>

I was too quick to acknowledge this patchset. It doesn't work.

This patchset fixes the crash, but it introduces another bug - when I type 
'reboot' on the console, it prints 'INIT: Switching to runlevel: 6' and 
then it gets stuck for 80 seconds before proceeding with the reboot. When 
I revert this patchset 'reboot' reboots the machine without any delay. 
This bug was reproduced on Debian 5 userspace on pa-risc.

Mikulas