Hi Paul, I would suggest the following patch for defer/route_refcnt.c (as in Listing 9.2). For the change in re_free, if we actually call free(3) on `rep', we will lose that piece of memory so that the READ_ONCE() at line 36 might see garbage value and will probably will not call abort(3), i.e., that is implementation specific behavior. And I don't see why will we have `old <=0`. I think I understand what that code mean but you might mean some other? Hopefully I will not be too picky. Thanks, Yubin ---------------------------------------- diff --git a/CodeSamples/defer/route_refcnt.c b/CodeSamples/defer/route_refcnt.c index 8a48faf..0d24e9d 100644 --- a/CodeSamples/defer/route_refcnt.c +++ b/CodeSamples/defer/route_refcnt.c @@ -36,7 +36,8 @@ DEFINE_SPINLOCK(routelock); static void re_free(struct route_entry *rep) { WRITE_ONCE(rep->re_freed, 1); - free(rep); + /* Will not actually free it. Just use the `re_freed' as a flag */ + /*free(rep);*/ } /* @@ -50,7 +51,6 @@ unsigned long route_lookup(unsigned long addr) struct route_entry **repp; unsigned long ret; -retry: repp = &route_list.re_next; rep = NULL; do { @@ -65,8 +65,6 @@ retry: if (READ_ONCE(rep->re_freed)) abort(); old = atomic_read(&rep->re_refcnt); - if (old <= 0) - goto retry; new = old + 1; } while (atomic_cmpxchg(&rep->re_refcnt, old, new) != old); -- To unsubscribe from this list: send the line "unsubscribe perfbook" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html