- ((((R)->next_to_clean > (R)->next_to_use) \
- ? 0 : (R)->count) + (R)->next_to_clean - (R)->next_to_use - 1)
+({ \
+ unsigned int clean = smp_load_acquire(&(R)->next_to_clean); \
+ unsigned int use = READ_ONCE((R)->next_to_use); \
+ (clean > use ? 0 : (R)->count) + clean - use - 1; \
+})