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

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Message-ID: <20160203083030.GD30520@swordfish>
Date:	Wed, 3 Feb 2016 17:30:30 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Byungchul Park <byungchul.park@....com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	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 (02/03/16 17:12), Byungchul Park wrote:
> 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?

sure,

	https://lkml.org/lkml/2015/10/26/16
and
	http://marc.info/?l=linux-kernel&m=145079206822115

	-ss