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

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Message-ID: <20180113073100.GB1701@tigerII.localdomain>
Date:   Sat, 13 Jan 2018 16:31:00 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tejun Heo <tj@...nel.org>,
        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

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