On Thu, Aug 31, 2017 at 03:22:05PM +1000, Michael Neuling wrote:

On Thu, 2017-08-31 at 06:36 +0200, Greg Kroah-Hartman wrote:

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

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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?

For me it crashed on boot.

Nathan said he's getting the crashes at runtime, randomly, but often.

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

but then reverted here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i d=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;#26 64604

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?

I'm not anymore. We found it was only triggered on a bogus CONFIG option combination. Once we removed that, it no longer happened.

The underlying bug was still there though.

Yep.. and the bug seems to trigger at runtime.

Mikey

-- Pasi