linux-kernel - Re: [PATCH v6 1/2] printk: Factor out buffering and irq work queuing in printk

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Message-ID: <20160314012157.GA8074@swordfish>
Date:	Mon, 14 Mar 2016 10:21:57 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Byungchul Park <byungchul.park@....com>
Cc:	akpm@...ux-foundation.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, akinobu.mita@...il.com, jack@...e.cz,
	sergey.senozhatsky.work@...il.com, peter@...leysoftware.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org
Subject: Re: [PATCH v6 1/2] printk: Factor out buffering and irq work queuing
 in printk_deferred

Hello Byungchul,

Sorry, I'll make sure I Cc you next time. Jan Kara's updated patch set

http://marc.info/?l=linux-kernel&m=145787625506342

it's quite close to what you have done in this patch, but Jan's
patch also solves a number of more likely to happen cases.

have time to take a look?

the lock debug patch in your series is different. can we settle
down async printk first and then return to it? it's not so simple...

On (03/11/16 19:37), Byungchul Park wrote:
[..]
>  int printk_deferred(const char *fmt, ...)
>  {
>  	va_list args;
>  	int r;
>  
>  	preempt_disable();
> +
>  	va_start(args, fmt);
> -	r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args);
> +	r = vprintk_deferred(fmt, args);
>  	va_end(args);
> +	printk_pending_output();
>  
> -	__this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
> -	irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
>  	preempt_enable();
>  
>  	return r;

vprintk_deferred() does vprintk_emit()->{spin_lock()} again? cosole_lock() is
moved out of sight, but logbug_lock is still there. wouldn't this (in the worst
case) result in endless loop after all? sorry if I'm missing something.

	-ss