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    SubjectRe: [PATCH] rcu: avoid checking for constant
    On Thu, Jan 12, 2012 at 06:11:44AM +0100, Jan Engelhardt wrote:
    > When compiling kernel or module code with -O0, "offset" is no longer
    > considered a constant, and therefore always triggers the build error
    > that BUILD_BUG_ON is defined to yield.
    >
    > What is the rationale between the forced constant check,
    > introduced in 9ab1544eb4196ca8d05c433b2eb56f74496b1ee3?
    [...]
    > --- a/include/linux/rcupdate.h
    > +++ b/include/linux/rcupdate.h
    > @@ -805,8 +805,6 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset)
    > {
    > typedef void (*rcu_callback)(struct rcu_head *);
    >
    > - BUILD_BUG_ON(!__builtin_constant_p(offset));
    > -
    > /* See the kfree_rcu() header comment. */
    > BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));

    The very next check after the one you removed will break if the
    compiler can't check the offset at compile time.

    - Josh Triplett


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