lockless_dereference() is planned to grow a sanity check to ensure that the input parameter is a pointer. __ref_is_percpu() passes in an unsinged long value which is a combination of a pointer and a flag. While it can be casted to a pointer lvalue, the casting looks messy and it's a special case anyway. Let's revert back to open-coding READ_ONCE() and explicit barrier.
This doesn't cause any functional changes. Signed-off-by: Tejun Heo <t...@kernel.org> Link: http://lkml.kernel.org/g/20160522185040.ga23...@p183.telecom.by Cc: Pranith Kumar <bobby.pr...@gmail.com> Cc: Alexey Dobriyan <adobri...@gmail.com> Cc: Peter Zijlstra <pet...@infradead.org> --- So, something like this. Please feel free to include in the series. Thanks. include/linux/percpu-refcount.h | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index 84f542d..1c7eec0 100644 --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -136,14 +136,12 @@ static inline bool __ref_is_percpu(struct percpu_ref *ref, * used as a pointer. If the compiler generates a separate fetch * when using it as a pointer, __PERCPU_REF_ATOMIC may be set in * between contaminating the pointer value, meaning that - * ACCESS_ONCE() is required when fetching it. - * - * Also, we need a data dependency barrier to be paired with - * smp_store_release() in __percpu_ref_switch_to_percpu(). - * - * Use lockless deref which contains both. + * READ_ONCE() is required when fetching it. */ - percpu_ptr = lockless_dereference(ref->percpu_count_ptr); + percpu_ptr = READ_ONCE(ref->percpu_count_ptr); + + /* paired with smp_store_release() in __percpu_ref_switch_to_percpu() */ + smp_read_barrier_depends(); /* * Theoretically, the following could test just ATOMIC; however,
