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Date: Tue, 23 Jan 2018 16:31:43 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup
Message-ID: <20180123073143.GB489@jagdpanzerIV>
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To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>, Tejun Heo <tj@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, 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, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

On (01/23/18 15:40), Sergey Senozhatsky wrote:
> 
> Why do we even use irq_work for printk_safe?
> 

... perhaps because of

wq: pool->lock -> printk -> call_console_drivers -> printk -> vprintk_safe -> wq: pool->lock

Which is a "many things have gone wrong" type of scenario. Maybe we
can workaround it somehow, hm. Tejun, can we have lockless WQ? ;)

	-ss

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