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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     Michal Hocko <mhocko@kernel.org>
CC:     Petr Mladek <pmladek@suse.com>, Greg KH <greg@kroah.com>,
        Pavel Machek <pavel@ucw.cz>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>, Jan Kara <jack@suse.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Byungchul Park <byungchul.park@lge.com>,
        Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH AUTOSEL for 4.14 015/161] printk: Add console owner and
 waiter logic to load balance console writes
Thread-Topic: [PATCH AUTOSEL for 4.14 015/161] printk: Add console owner and
 waiter logic to load balance console writes
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Date:   Tue, 17 Apr 2018 14:36:44 +0000
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On Tue, Apr 17, 2018 at 04:22:46PM +0200, Michal Hocko wrote:
>On Tue 17-04-18 13:39:33, Sasha Levin wrote:
>[...]
>> But mm/ commits don't come only from these people. Here's a concrete
>> example we can discuss:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commi=
t/?id=3Dc61611f70958d86f659bca25c02ae69413747a8d
>
>I would be really careful. Because that reqiures to audit all callers to
>be compliant with the change. This is just _too_ easy to backport
>without noticing a failure. Now consider the other side. Is there any
>real bug report backing this? This behavior was like that for quite some
>time but I do not remember any actual bug report and the changelog
>doesn't mention one either. It is about theoretical problem.

https://lkml.org/lkml/2018/3/19/430

There's even a fun little reproducer that allowed me to confirm it's an
issue (at least) on 4.15.

Heck, it might even qualify as a CVE.

>So if this was to be merged to stable then the changelog should contain
>a big fat warning about the existing users and how they should be
>checked.

So what I'm asking is why *wasn't* it sent to stable? Yes, it requires
additional work backporting this, but what I'm saying is that this
didn't happen at all.

>Besides that I can see Reviewed-by: akpm and Andrew is usually very
>careful about stable backports so there probably _was_ a reson to
>exclude stable.
>--=20
>Michal Hocko
>SUSE Labs=