Date: Sat, 13 Jan 2018 16:31:00 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Tejun Heo <tj@kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        akpm@linux-foundation.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>, Michal Hocko <mhocko@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jan Kara <jack@suse.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        rostedt@home.goodmis.org, Byungchul Park <byungchul.park@lge.com>,
        Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup
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On (01/12/18 13:55), Petr Mladek wrote:
[..]
> > I'm not fixing console_unlock(), I'm fixing printk(). BTW, all my
> > kernels are CONFIG_PREEMPT (I'm a RT guy), my mind thinks more about
> > PREEMPT kernels than !PREEMPT ones.
> 
> I would say that the patch improves also console_unlock() but only in
> non-preemttive context.
> 
> By other words, it makes console_unlock() finite in preemptible context
> (limited by buffer size). It might still be unlimited in
> non-preemtible context.

could you elaborate a bit?

[..]
> > > reverting 6b97a20d3a7909daa06625d4440c2c52d7bf08d7 may be the right
> > > thing after all.
> > 
> > I would analyze that more before doing so. Because with my patch, I
> > think we make those that can do long prints (without triggering a
> > watchdog), the ones most likely doing the long prints.
> 
> IMHO, it might make sense because it would help to see the messages
> faster. But I would prefer to handle this separately because it
> might also increase the risk of softlockups. Therefore it might
> cause regressions.
> 
> We should also take into account the commit 8d91f8b15361dfb438ab6
> ("printk: do cond_resched() between lines while outputting to
> consoles"). It has the same effect for console_lock() callers.

I replied in another email.

	-ss