Re: linux-next: build failure after merge of the rcu tree

Paul E. McKenney
2015-07-17T21:33:42Z

On Fri, Jul 17, 2015 at 09:51:31PM +0200, Ingo Molnar wrote:
>
> * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
>
> > And here is a prototype patch, which I intend to merge with the existing patch
> > that renames rcu_lockdep_assert() to RCU_LOCKDEP_WARN(). I will also queue a
> > revert of the patch below for 4.4.
> >
> > Thoughts?
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 41c49b12fe6d..663d6e028c3d 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -536,9 +536,29 @@ static inline int rcu_read_lock_sched_held(void)
> >
> > #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
> >
> > +/* Deprecate the rcu_lockdep_assert() macro. */
> > +static inline void __attribute((deprecated)) deprecate_rcu_lockdep_assert(void)
> > +{
> > +}
> > +
> > #ifdef CONFIG_PROVE_RCU
> >
> > /**
> > + * rcu_lockdep_assert - emit lockdep splat if specified condition not met
> > + * @c: condition to check
> > + * @s: informative message
> > + */
> > +#define rcu_lockdep_assert(c, s) \
> > + do { \
> > + static bool __section(.data.unlikely) __warned; \
> > + deprecate_rcu_lockdep_assert(); \
> > + if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
> > + __warned = true; \
> > + lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
> > + } \
>
> Btw., out of general macro paranoia I'd write such constructs as something like:
>
> if (!(c) && debug_lockdep_rcu_enabled() && !__warned) { \
>
> I.e. always evaluate 'c' even if debugging is off. This way if the construct is
> fed an expression with a side effect (bad idea!) then it still works regardless of
> whether the warning triggered already or not.

If you feel strongly about this, I will need to make lockdep_is_held()
be defined when lockdep is disabled. Easy enough to do, just thought
I should double-check.

> But this construct is OK too to me, so feel free to add my:
>
> Reviewed-by: Ingo Molnar <mingo@kernel.org>

Thank you!

Thanx, Paul