linux-kernel - Re: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs rcu_read

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Date:	Fri, 21 Sep 2007 16:30:27 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	"Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Nick Piggin" <nickpiggin@...oo.com.au>
Subject: Re: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs
 rcu_read_lock()

On Fri, 21 Sep 2007 10:15:10 -0400 "Dmitry Torokhov"
<dmitry.torokhov@...il.com> wrote:

> On 9/20/07, Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> > On Thu, Sep 20, 2007 at 01:31:35PM -0400, Dmitry Torokhov wrote:
> > >
> > > OK, then what is the purpose of synchronize_sched() in -rt?
> >
> > To wait for all preempt-disable, irq-disable, hard-irq, and SMI/NMI code
> > sequences to complete.
> 
> OK, so what spin_lock_irq[save]? Does is disable IRQs in -rt or not anymore?
> If IRQs are disabled it appears that I can continue using synchronize_sched().

No it will not disable IRQs anymore.

> >
> > > You really need to provide users with a replacement. There are several
> > > drivers that use it and for example r8169 is not what you'd call a
> > > 'low performer'.
> >
> > I did look at making a synchronize_all_irq() some time back, and all
> > the approaches I came up with at the time were busted.
> >
> > But I just took another look, and I think I see a way to handle it.
> > Either that, or I simply forgot the way in which this approach is
> > broken...
> >
> > I will stare at is some more.
> >
> 
> Thank you.

I think the patch posted by Paul earlier today should work.
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