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);
--
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