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

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Date:   Wed, 17 Jan 2018 11:24:09 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Tejun Heo <tj@...nel.org>, 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>,
        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 (01/16/18 11:19), Petr Mladek wrote:
[..]
> > [1] https://marc.info/?l=linux-mm&m=145692016122716
> > Fixes: 6b97a20d3a79 ("printk: set may_schedule for some of console_trylock() callers")
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> > Reported-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> 
> IMHO, this is a step in the right direction.
> 
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> 
> I'll wait for Steven's review and push this into printk.git.
> I'll also add your Acks for the other patches.
> 
> Thanks for the patch and the various observations.

thanks!


a side note,

our console output is still largely preemptible. a typical system
acquires console_sem via console_lock() all the time, so we still
can have "where is my printk output?" cases.


for instance, my IDLE PREEMPT x86 box, has the following stats

uptime 15 min

# of console_lock() calls: 10981          // can sleep under console_sem
# of vprintk_emit() calls: 825            // cannot sleep under console_sem

	-ss