linux-kernel - Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes"

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Message-ID: <20181001162958.3b8e4640@gandalf.local.home>
Date:   Mon, 1 Oct 2018 16:29:58 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Pavel Machek <pavel@....cz>
Cc:     Daniel Wang <wonderfly@...gle.com>, stable@...r.kernel.org,
        pmladek@...e.com, Alexander.Levin@...rosoft.com,
        akpm@...ux-foundation.org, byungchul.park@....com,
        dave.hansen@...el.com, hannes@...xchg.org, jack@...e.cz,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mathieu.desnoyers@...icios.com, mgorman@...e.de, mhocko@...nel.org,
        penguin-kernel@...ove.SAKURA.ne.jp, peterz@...radead.org,
        tj@...nel.org, torvalds@...ux-foundation.org, vbabka@...e.cz,
        xiyou.wangcong@...il.com, pfeiner@...gle.com
Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console
 owner and waiter logic to load balance console writes"

On Mon, 1 Oct 2018 22:13:10 +0200
Pavel Machek <pavel@....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