| Message ID | 20200916184528.498184-7-kuba@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | None | expand |
On Wed, Sep 16, 2020 at 11:45:27AM -0700, Jakub Kicinski wrote: > When CONFIG_LOCKDEP is not set, lock_is_held() and lockdep_is_held() > are not declared or defined. This forces all callers to use ifdefs > around these checks. > > Recent RCU changes added a lot of lockdep_is_held() calls inside > rcu_dereference_protected(). rcu_dereference_protected() hides > its argument on !LOCKDEP builds, but this may lead to unused variable > warnings. > > Provide forward declarations of lock_is_held() and lockdep_is_held() > but never define them. This way callers can keep them visible to > the compiler on !LOCKDEP builds and instead depend on dead code > elimination to remove the references before the linker barfs. > > We need lock_is_held() for RCU. > > Signed-off-by: Jakub Kicinski <kuba@kernel.org> > -- > CC: peterz@infradead.org > CC: mingo@redhat.com > CC: will@kernel.org > --- > include/linux/lockdep.h | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h > index 6a584b3e5c74..6b5bbc536bf6 100644 > --- a/include/linux/lockdep.h > +++ b/include/linux/lockdep.h > @@ -371,6 +371,12 @@ static inline void lockdep_unregister_key(struct lock_class_key *key) > > #define lockdep_depth(tsk) (0) > > +/* > + * Dummy forward declarations, allow users to write less ifdef-y code > + * and depend on dead code elimination. > + */ > +int lock_is_held(const void *); extern int lock_is_held(const struct lockdep_map *); > +int lockdep_is_held(const void *); extern I suppose we can't pull the lockdep_is_held() definition out from under CONFIG_LOCKDEP because it does the ->dep_map dereference and many types will simply not have that member. > #define lockdep_is_held_type(l, r) (1) > > #define lockdep_assert_held(l) do { (void)(l); } while (0)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 6a584b3e5c74..6b5bbc536bf6 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -371,6 +371,12 @@ static inline void lockdep_unregister_key(struct lock_class_key *key) #define lockdep_depth(tsk) (0) +/* + * Dummy forward declarations, allow users to write less ifdef-y code + * and depend on dead code elimination. + */ +int lock_is_held(const void *); +int lockdep_is_held(const void *); #define lockdep_is_held_type(l, r) (1) #define lockdep_assert_held(l) do { (void)(l); } while (0)
When CONFIG_LOCKDEP is not set, lock_is_held() and lockdep_is_held() are not declared or defined. This forces all callers to use ifdefs around these checks. Recent RCU changes added a lot of lockdep_is_held() calls inside rcu_dereference_protected(). rcu_dereference_protected() hides its argument on !LOCKDEP builds, but this may lead to unused variable warnings. Provide forward declarations of lock_is_held() and lockdep_is_held() but never define them. This way callers can keep them visible to the compiler on !LOCKDEP builds and instead depend on dead code elimination to remove the references before the linker barfs. We need lock_is_held() for RCU. Signed-off-by: Jakub Kicinski <kuba@kernel.org> -- CC: peterz@infradead.org CC: mingo@redhat.com CC: will@kernel.org --- include/linux/lockdep.h | 6 ++++++ 1 file changed, 6 insertions(+)