On Fri, Jan 08, 2016 at 07:53:41AM -0800, Paul E. McKenney wrote: > commit 61822ff81839ee3c5b6094ce348944d972b87892 > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > Date: Fri Jan 8 07:43:50 2016 -0800 > > rcu: Document unique-name limitation for DEFINE_STATIC_SRCU() > > SRCU uses per-CPU variables, and DEFINE_STATIC_SRCU() uses a static > per-CPU variable. However, per-CPU variables have significant > restrictions, for example, names of per-CPU variables must be globally > unique, even if declared static. These restrictions carry over to > DEFINE_STATIC_SRCU(), and this commit therefore documents these > restrictions. > > Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> > Reported-by: kbuild test robot <fengguang.wu@xxxxxxxxx> > Suggested-by: Boqun Feng <boqun.feng@xxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > diff --git a/include/linux/srcu.h b/include/linux/srcu.h > index f5f80c5643ac..dc8eb63c6568 100644 > --- a/include/linux/srcu.h > +++ b/include/linux/srcu.h > @@ -99,8 +99,23 @@ void process_srcu(struct work_struct *work); > } > > /* > - * define and init a srcu struct at build time. > - * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it. > + * Define and initialize a srcu struct at build time. > + * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it. > + * > + * Note that although DEFINE_STATIC_SRCU() hides the name from other > + * files, the per-CPU variable rules nevertheless require that the > + * chosen name be globally unique. These rules also prohibit use of > + * DEFINE_STATIC_SRCU() within a function. If these rules are too > + * restrictive, declare the srcu_struct manually. For example, in > + * each file: > + * > + * static struct srcu_struct my_srcu; > + * > + * Then, before the first use of each my_srcu, manually initialize it: > + * > + * init_srcu_struct(&my_srcu); > + * > + * See include/linux/percpu-defs.h for the rules on per-CPU variables. FWIW, Reviewed-by: Tejun Heo <tj@xxxxxxxxxx> Thanks Stephen for posting the rules around static percpu definitions. I wonder whether there is a better way to tell people what's going on. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
