linux-kernel - Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within up()

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Message-ID: <20160203081242.GA32743@X58A-UD3R>
Date:	Wed, 3 Feb 2016 17:12:42 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>, willy@...ux.intel.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	akinobu.mita@...il.com, jack@...e.cz, peter@...leysoftware.com,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within
 up()

On Wed, Feb 03, 2016 at 04:42:23PM +0900, Sergey Senozhatsky wrote:
> On (02/03/16 08:28), Ingo Molnar wrote:
> [..]
> > So why not move printk away from semaphores? Semaphores are classical constructs 
> > that have legacies and are somewhat non-obvious to use, compared to modern, 
> > simpler locking primitives. I'd not touch their implementation, unless we are 
> > absolutely sure this is a safe optimization.
> 
> semaphore's spin_lock is not the only spin lock that printk acquires. it also takes the
> logbuf_lock (and different locks in console drivers (up to console driver)).
> 
> Jan Kara posted a patch that offloads printing job (console_trylock()-console_unlock())
> from printk() call (when printk can offload it). so semaphore and console driver's locks
> will go away (mostly) with Jan's patch. logbug spin_lock, however, will stay.

It sounds good. Could you teach me how to see the patch by Jan?

> 
> 	-ss