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

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Date:	Thu, 01 Apr 2010 18:36:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Avi Kivity <avi@...hat.com>,
	Andrea Arcangeli <aarcange@...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>
Subject: Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in
 mmu_take_all_locks()

On Thu, 2010-04-01 at 09:15 -0700, Paul E. McKenney wrote:
> > I don't understand.  I thought the problem was that the locks were
> > taken inside an rcu critical section; switching to srcu would fix
> > that.  But how is call_rcu_preempt() related?  Grepping a bit, what
> > is call_rcu_preempt()?  my tree doesn't have it.
> 
> I believe that Peter is referring to the RCU implementation you get
> with CONFIG_TREE_PREEMPT_RCU, which currently depends on CONFIG_PREEMPT.
> The other implementation is CONFIG_TREE_RCU, which is usually called
> "classic RCU". 

Right, so I've been nudging Paul a while to make it so that we always
have preemptible rcu available and that only the default interface
switches between sched/classic and preempt.

Currently we already have:

call_rcu_sched()
call_rcu_bh()
call_rcu()	(depends on CONFIG_PREEMPT_RCU)

I'm saying it would be nice to also have:

call_rcu_preempt()



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