linux-kernel - Re: [PATCH 01/13] powerpc: Add rcu_read_lock() to gup

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Message-ID: <1271559996.14589.9.camel@mulgrave.site>
Date:	Sat, 17 Apr 2010 22:06:36 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast()
 implementation

On Fri, 2010-04-16 at 09:45 -0700, Paul E. McKenney wrote:
> o	mutex_lock(): Critical sections need not guarantee
> 	forward progress, as general blocking is permitted.

This isn't quite right.  mutex critical sections must guarantee eventual
forward progress against the class of other potential acquirers of the
mutex otherwise the system will become either deadlocked or livelocked.

James


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