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Date: Thu, 2 Feb 2012 13:44:19 +0000
From: Arnd Bergmann <arnd@...db.de>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Prarit Bhargava <prarit@...hat.com>,
"Greg Kroah-Hartman" <greg@...ah.com>,
Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH 1/2] lkdtm: use atomic_t to replace count_lock
On Thursday 02 February 2012, Cong Wang wrote:
> > In order to have an atomic here, you have to use a loop around
> > atomic_cmpxchg, like
> >
> >
> > int old, new;
> > old = atomic_read(&count);
> > do {
> > new = old ? old - 1 : cpoint_count;
> > old = cmpxchg(&count, old, new);
> > } while (old != new);
> >
> > I suppose you could also just keep the spinlock and move lkdtm_do_action()
> > outside of it?
>
> If we still need spinlock, I think we don't need to bother atomic_t at all.
Yes, it's one or the other: If you use the cmpxchg loop, you don't need a
spinlock and vice versa.
Arnd
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