Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> static inline void *assoc_array_ptr_to_leaf(const struct assoc_array_ptr *x)
> {
> - return (void *)((unsigned long)x & ~ASSOC_ARRAY_PTR_TYPE_MASK);
> + return (void *)((unsigned long)READ_ONCE(x) & /* Address dependency. */
> + ~ASSOC_ARRAY_PTR_TYPE_MASK);
> }
This is the wrong place to do this. assoc_array_ptr_to_leaf() is effectively
no more than a special cast; it removes a metadata bit from a pointer. x is
the value we're modifying, not *x, and x was read by the caller.
> static inline
> unsigned long __assoc_array_ptr_to_meta(const struct assoc_array_ptr *x)
> {
> - return (unsigned long)x &
> + return (unsigned long)READ_ONCE(x) & /* Address dependency. */
> ~(ASSOC_ARRAY_PTR_SUBTYPE_MASK | ASSOC_ARRAY_PTR_TYPE_MASK);
> }
Ditto.
> - ptr = READ_ONCE(node->slots[slot]);
> + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
> has_meta |= (unsigned long)ptr;
> if (ptr && assoc_array_ptr_is_leaf(ptr)) {
> - /* We need a barrier between the read of the pointer
> - * and dereferencing the pointer - but only if we are
> - * actually going to dereference it.
> - */
> - smp_read_barrier_depends();
> -
For example, you can see the READ_ONCE() here; that is already done.
Can you also not just delete the comment, but rephrase it to indicate that a
barrier is necessary and it's done by READ_ONCE(), please?
David
