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

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Date:   Thu, 31 Aug 2017 06:36:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pasi Kärkkäinen <pasik@....fi>
Cc:     Mikulas Patocka <mpatocka@...hat.com>,
        Michael Neuling <mikey@...ling.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Peter Hurley <peter@...leysoftware.com>,
        Nathan March <nathan@...net>, centos-virt@...tos.org,
        linux-kernel@...r.kernel.org
Subject: Re: Status of reverted Linux patch "tty: Fix ldisc crash on reopened
 tty", Linux 4.9 kernel frequent crashes

On Wed, Aug 30, 2017 at 11:10:14PM +0300, Pasi Kärkkäinen wrote:
> 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".

Crashes with "normal" operation, or crashes when running a fuzzer or
other type of program?

> 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.

I don't know of anyone working on it, want to do it yourself?

thanks,

greg k-h