linux-kernel - Status of reverted Linux patch "tty: Fix ldisc crash on reopened tty", Linux 4.9 kernel frequent crashes

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Message-ID: <20170830201014.GO4090@reaktio.net>
Date:   Wed, 30 Aug 2017 23:10:14 +0300
From:   Pasi Kärkkäinen <pasik@....fi>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Michael Neuling <mikey@...ling.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Peter Hurley <peter@...leysoftware.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nathan March <nathan@...net>, centos-virt@...tos.org,
        linux-kernel@...r.kernel.org
Subject: Status of reverted Linux patch "tty: Fix ldisc crash on reopened
 tty", Linux 4.9 kernel frequent crashes

Hello everyone,

Recently Nathan March reported on centos-virt list he's getting frequent Linux kernel crashes with Linux 4.9 LTS kernel because of the missing patch "tty: Fix ldisc crash on reopened tty".

The patch was already merged upstream here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=71472fa9c52b1da27663c275d416d8654b905f05

but then reverted here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=896d81fefe5d1919537db2c2150ab6384e4a6610

Nathan confirmed if he applies the patch from 71472fa9c52b1da27663c275d416d8654b905f05 to his Linux 4.9 LTS kernel the bug/problem goes away, so the patch (or similar fix) is still needed, at least for 4.9 LTS kernel.

Mikulas reported he's able to trigger the same crash on Linux 4.10:
https://www.spinics.net/lists/kernel/msg2440637.html
https://lists.gt.net/linux/kernel/2664604?search_string=ldisc%20reopened;#2664604

Michael Neuling reported he's able to trigger the bug on PowerPC:
https://lkml.org/lkml/2017/3/10/1582

So now the question is.. is anyone currently working on getting this patch fixed and applied upstream? I think one of the problems earlier was being able to reliable reproduce the crash.. Nathan says he's able to reproduce it many times per week on his environment on x86_64.

Thanks a lot,

-- Pasi