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

Ingo Molnar
2015-07-18T02:40:02Z

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> 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. [...]

No need - if it goes deeper then I wouldn't worry.

Thanks,

Ingo