linux-kernel - Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all

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Date:	Thu, 1 Apr 2010 18:08:51 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Avi Kivity <avi@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	Kent Overstreet <kent.overstreet@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in
 mmu_take_all_locks()

On Thu, Apr 01, 2010 at 05:56:46PM +0200, Peter Zijlstra wrote:
> I would much rather we make call_rcu_preempt() available at all times.

srcu is needed only for XPMEM to make the mmu notifier handlers
sleepable. Ignore it for now, it can be done later. The locks you're
changing are always taken _before_ the mmu notifier_range_start and
always after the mmu_notifier_range_end, so srcu can be done later...

It's orthogonal issue, but the moment these locks are sleepable it
simply worth to switch mmu notifiers to srcu to accommodate XPMEM.
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