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

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Date:	Fri, 16 Apr 2010 16:54:51 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.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 Thu, 2010-04-15 at 07:28 -0700, Paul E. McKenney wrote:
> 
> Of course, with call_rcu_sched(), the corresponding RCU read-side
> critical
> sections are non-preemptible.  Therefore, in CONFIG_PREEMPT_RT, these
> read-side critical sections must use raw spinlocks.
> 
> Can the code in question accommodate these restrictions? 

What we protect against is always code that hard-disable IRQs (though
there seem to be a bug in the hugepages code there...). Would that
work ?

Cheers,
Ben.

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