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Date:   Mon, 1 Oct 2018 16:29:58 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Daniel Wang <wonderfly@google.com>, stable@vger.kernel.org,
        pmladek@suse.com, Alexander.Levin@microsoft.com,
        akpm@linux-foundation.org, byungchul.park@lge.com,
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        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        mathieu.desnoyers@efficios.com, mgorman@suse.de, mhocko@kernel.org,
        penguin-kernel@I-love.SAKURA.ne.jp, peterz@infradead.org,
        tj@kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz,
        xiyou.wangcong@gmail.com, pfeiner@google.com
Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console
 owner and waiter logic to load balance console writes"
Message-ID: <20181001162958.3b8e4640@gandalf.local.home>
In-Reply-To: <20181001201309.GA9835@amd>
References: <20180927194601.207765-1-wonderfly@google.com>
        <20181001152324.72a20bea@gandalf.local.home>
        <20181001201309.GA9835@amd>
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On Mon, 1 Oct 2018 22:13:10 +0200
Pavel Machek <pavel@ucw.cz> wrote:

> > > [1] https://lore.kernel.org/lkml/20180409081535.dq7p5bfnpvd3xk3t@pathway.suse.cz/T/#u
> > > 
> > > Serial console logs leading up to the deadlock. As can be seen the stack trace
> > > was incomplete because the printing path hit a timeout.  
> > 
> > I'm fine with having this backported.  
> 
> Dunno. Is the patch perhaps a bit too complex? This is not exactly
> trivial bugfix.
> 
> pavel@duo:/data/l/clean-cg$ git show dbdda842fe96f | diffstat
>  printk.c |  108
>  ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 
> I see that it is pretty critical to Daniel, but maybe kernel with
> console locking redone should no longer be called 4.4?

But it prevents a deadlock.

I usually weigh backporting as benefit vs risk. And I believe the
benefit outweighs the risk in this case.

-- Steve