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SubjectRe: [RFC/PATCH] debug workqueue deadlocks with lockdep

* Johannes Berg <johannes@sipsolutions.net> wrote:

> > > +#define create_workqueue(name) \
> > > +({ \
> > > + static struct lock_class_key __key; \
> > > + struct workqueue_struct *__wq; \
> > > + \
> > > + __wq = __create_workqueue((name), 0, 0, &__key); \
> > > + __wq; \
> > > +})
> >
> > Why do we need __wq ?
>
> No particular reason I think, I copied some other code doing it that
> way.

yep, should be fine doing this:

#define create_workqueue(name) \
({ \
static struct lock_class_key __key; \
\
__create_workqueue((name), 0, 0, &__key); \
})
(and the return value of __create_workqueue() will be the 'return value'
of the macro as well.)

> > + extern struct workqueue_struct *__create_workqueue_key(..., key);
> > + #define __create_workqueue(...) \
> > + static struct lock_class_key __key; \
> > + __create_workqueue_key(..., key); \
> >
> > but this is a matter of taste.

the above macro should at minimum be encapsulated with
do { ... } while (0) so that __create_workqueue() is a single C
statement.
Ingo
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