linux-kernel - Re: tty: panic in tty_ldisc

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Date:   Fri, 3 Mar 2017 08:36:13 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jslaby@...e.com>, LKML <linux-kernel@...r.kernel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: tty: panic in tty_ldisc_restore

On Thu, Mar 2, 2017 at 8:37 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>> >> This is hurting us badly.
>> >
>> > Really?  How?  Are you hitting this a lot?  Why now and never before?
>> > Are you really out of memory?
>>
>>
>> This crashes our test bots a lot.
>> Why now... I don't have exact answer. Probably a combination of fuzzer
>> figuring out some magic sequences of syscalls and increased memory
>> consumption due to something (again maybe due to fuzzer figuring out
>> how to eat more memory).
>
> If the fuzzer is suddenly eating more memory, you should be seeing lots
> of other problems  right?  This can't be the only thing that has issues
> with memory allocation failures?


I remember 2 or 3 that started happenning roughly at the same time:
https://groups.google.com/forum/#!msg/syzkaller/tIx42qCVklk/fh0qjUboBgAJ
https://groups.google.com/forum/#!msg/syzkaller/vp1neyeoA8A/Is8aPdrpBgAJ
Both were quickly fixed.
There is strong bias towards failing larger, multi-page allocations.
so it's not that we are failing _all_ allocations in kernel code.