linux-kernel - Re: [PATCH v5 1/2] printk: Add console owner and waiter logic to load balance console writes

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Message-ID: <20180118220323.GC17196@amd>
Date:   Thu, 18 Jan 2018 23:03:24 +0100
From:   Pavel Machek <pavel@....cz>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     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>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/2] printk: Add console owner and waiter logic to
 load balance console writes

Hi!

> > By other words, this deadlock was there even before. Such
> > deadlocks are prevented by using printk_deferred() in
> > the sections guarded by the lock A.
> 
> Petr,
> 
> Please add this here:
> 
> ====
> 
> To demonstrate the issue, this module has been shown to lock up a
> system with 4 CPUs and a slow console (like a serial console). It is
> also able to lock up a 8 CPU system with only a fast (VGA) console, by
> passing in "loops=100". The changes in this commit prevent this module
> from locking up the system.
> 
> #include <linux/module.h>
> #include <linux/delay.h>
> #include <linux/sched.h>
> #include <linux/mutex.h>
> #include <linux/workqueue.h>
> #include <linux/hrtimer.h>

Programs in commit messages. Not preffered way to distribute code, I'd
say. What about putting it into kernel selftests directory or
something like that?
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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