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

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Date:   Mon, 22 Jan 2018 19:28:57 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Tejun Heo <tj@...nel.org>, Petr Mladek <pmladek@...e.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 (01/22/18 17:56), Sergey Senozhatsky wrote:
[..]
> Assume the following,

But more importantly we are missing another huge thing - console_unlock().

Suppose:

	console_lock();
	<< preemption >>
						printk
						printk
						..
						printk
	console_unlock()
	 for (;;) {
		call_console_drivers()
		   dump_stack
		   queue IRQ work

		IRQ work >>
		   flush_printk_safe
		   printk_deferred()
		   ...
		   printk_deferred()
		<< iret
	 }

This should explode: sleepable console_unlock() may reschedule,
printk_safe flush bypasses recursion checks.

	-ss