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Date:   Wed, 19 Sep 2018 13:35:16 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Dmitry Safonov <dima@arista.com>
cc:     linux-kernel@vger.kernel.org,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Daniel Axtens <dja@axtens.net>,
        Dmitry Vyukov <dvyukov@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Michael Neuling <mikey@neuling.org>,
        Nathan March <nathan@gt.net>,
        =?ISO-8859-15?Q?Pasi_K=E4rkk=E4inen?= <pasik@iki.fi>,
        Peter Hurley <peter@hurleysoftware.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rong, Chen" <rong.a.chen@intel.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Tan Xiaojun <tanxiaojun@huawei.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        stable@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, Jiri Slaby <jslaby@suse.cz>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
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Subject: Re: [PATCHv5 0/7] tty: Hold write ldisc sem in tty_reopen()
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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@redhat.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