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    SubjectRe: [PATCH] md: do not use ++ in rcu_dereference() argument
    On Thu, Sep 09, 2010 at 05:14:43PM +0200, Arnd Bergmann wrote:
    > 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.

    Hmmm... One approach would be have a secondary macro that was:

    #define __rcu_dereference_check_sparse(p, space) \
    (void) (((typeof (*p) space *)p) == p);

    when running sparse and:

    #define __rcu_dereference_check_sparse(p, space)

    otherwise.

    Would that do the trick?

    Thanx, Paul


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