linux-kernel - Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

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Message-ID: <20180116194456.GS3460072@devbig577.frc2.facebook.com>
Date:   Tue, 16 Jan 2018 11:44:56 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        Cong Wang <xiyou.wangcong@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        rostedt@...e.goodmis.org, Byungchul Park <byungchul.park@....com>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

Hello, Steven.

On Thu, Jan 11, 2018 at 09:55:47PM -0500, Steven Rostedt wrote:
> All I did was start off a work queue on each CPU, and each CPU does one
> printk() followed by a millisecond sleep. No 10,000 printks, nothing
> in an interrupt handler. Preemption is disabled while the printk
> happens, but that's normal.
> 
> This is much closer to an OOM happening all over the system, where OOMs
> stack dumps are occurring on different CPUS.

OOMs can't happen all over the system.  It can only happen on a single
CPU at a time.  If you're printing from multiple CPUs, your solution
would work great.  That is the situation your patches are designed to
address to begin with.  That isn't the problem that I reported tho.  I
understand that your solution works for that class of problems and
that is great.  I really wish that it could address the other class of
problems too tho, and it doesn't seem like it would be that difficult
to cover both cases, right?

Thanks.

-- 
tejun