Re: [PATCH] md: do not use ++ in rcu_dereference() argument

Arnd Bergmann
2010-09-09T15:14:43Z

On Tuesday 07 September 2010, Paul E. McKenney wrote:
> On Tue, Sep 07, 2010 at 10:00:58PM +0200, Arnd Bergmann wrote:
> > On Tuesday 07 September 2010 21:21:55 Kulikov Vasiliy wrote:
> > > #define __rcu_dereference_check(p, c, space) \
> > > ({ \
> > > typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
> > > ^
> > > rcu_lockdep_assert(c); \
> > > (void) (((typeof (*p) space *)p) = p); \
> > > ^ ^
> > > smp_read_barrier_depends(); \
> > > ((typeof(*p) __force __kernel *)(_________p1)); \
> > > })
> > >
> > > If I understand this, it is evaluated three times, right?
> >
> > Yes, that looks like my own fault, I added that :(
> >
> > This patch seems to fix it, but I need to think about it some more
> > to make sure it still does everything we need.
>
> Let me know when you are satisfied with it, and then I will pick it up.

I guess it would be good to put it in now. I haven't had the time
to try out all cases, but the current code in -next is definitely
broken, so please put the fix in now.

Arnd