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Date:   Thu, 18 Jan 2018 14:42:51 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Tejun Heo <tj@kernel.org>, Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        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
Message-ID: <20180118054251.GB6529@jagdpanzerIV>
References: <20180111045817.GA494@jagdpanzerIV>
 <20180111093435.GA24497@linux.suse>
 <20180111103845.GB477@jagdpanzerIV>
 <20180111112908.50de440a@vmware.local.home>
 <20180111203057.5b1a8f8f@gandalf.local.home>
 <20180111215547.2f66a23a@gandalf.local.home>
 <20180116194456.GS3460072@devbig577.frc2.facebook.com>
 <20180117091208.ezvuhumnsarz5thh@pathway.suse.cz>
 <20180117151509.GT3460072@devbig577.frc2.facebook.com>
 <20180117121251.7283a56e@gandalf.local.home>
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On (01/17/18 12:12), Steven Rostedt wrote:
[..]
>  /*
>   * Can we actually use the console at this time on this cpu?
> @@ -2333,6 +2390,7 @@ void console_unlock(void)
>  
>  	for (;;) {
>  		struct printk_log *msg;
> +		bool offload;
>  		size_t ext_len = 0;
>  		size_t len;
>  
> @@ -2393,15 +2451,20 @@ void console_unlock(void)
>  		 * waiter waiting to take over.
>  		 */
>  		console_lock_spinning_enable();
> +		offload = recursion_check_start();
>  
>  		stop_critical_timings();	/* don't trace print latency */
>  		call_console_drivers(ext_text, ext_len, text, len);
>  		start_critical_timings();
>  
> +		recursion_check_finish(offload);
> +
>  		if (console_lock_spinning_disable_and_check()) {
>  			printk_safe_exit_irqrestore(flags);
>  			return;
>  		}
> +		if (offload)
> +			kick_offload_thread();
>  
>  		printk_safe_exit_irqrestore(flags);
		^^^^^^^^^^^^^^^^

but we call console drivers in printk_safe.
printk -> console_drivers -> printk will be
redirected to this-CPU printk_safe buffer.

	-ss