linux-kernel - Re: [PATCH] Convert preempt_disabled in module.c to rcu read lock

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Date:	Thu, 23 Sep 2010 10:37:08 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	paulmck@...ux.vnet.ibm.com, tglx@...utronix.de
Subject: Re: [PATCH] Convert preempt_disabled in module.c to rcu read lock

On Wed, 22 Sep 2010 10:37:20 pm Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> Thomas Gleixner pointed out that the list_for_each_rcu()
> in module really need to use RCU read lock, not preempt disable.
> This is especially needed for the preemptive RCU code.
> >From what I understand the only reason for the preemption
> disabling is to protect against rcu, so using rcu_read_lock()
> is correct.

The preempt_disable() also protects against stop_machine() on
module remove.

I haven't been following the RCU story, but we were always slightly
abusing the infrastructure here just to do lockless insert.  If
list_for_each_entry_rcu() is changing, perhaps we need to open-code
the old version here?

Rusty.
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