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

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Date:   Thu, 18 Jan 2018 14:42:51 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Tejun Heo <tj@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.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>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

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