On 25 Jan 2018, at 12:08, Kristof Provost wrote:
> On 25 Jan 2018, at 11:34, Ian Lepore wrote:
>> On Wed, 2018-01-24 at 16:13 -0800, Gleb Smirnoff wrote:
>>> (r328313)
>>> K> @@ -1613,6 +1613,7 @@ int
>>> K> pf_unlink_state(struct pf_state *s, u_int flags)
>>> K> {
>>> K> struct pf_idhash *ih = &V_pf_idhash[PF_IDHASH(s)];
>>> K> + int last;
>>> K>
>>> K> if ((flags & PF_ENTER_LOCKED) == 0)
>>> K> PF_HASHROW_LOCK(ih);
>>> K> @@ -1653,7 +1654,8 @@ pf_unlink_state(struct pf_state *s, u_int
>>> flags)
>>> K> PF_HASHROW_UNLOCK(ih);
>>> K>
>>> K> pf_detach_state(s);
>>> K> - refcount_release(&s->refs);
>>> K> + last = refcount_release(&s->refs);
>>> K> + KASSERT(last == 0, ("Incorrect state reference count"));
>>> K>
>>> K> return (pf_release_state(s));
>>> K> }
>>>
>>> IMHO, we shouldn't emit extra code to please Coverity. We can mark
>>> it
>>> as a false positive in the interface. It may make sense to add a
>>> comment
>>> for a human to explain why return isn't checked here.
>>>
>>
>> Not to mention that when KASSERT compiles to nothing, what you're
>> left
>> with is a "defined but not used" warning for 'last'.
>>
> I’d really like to keep the KASSERT(), because this is the sort of
> thing that could go wrong, and the assertion would be helpful.
>
> I suppose I could wrap last in #ifdef INVARIANTS, but that’s rather
> ugly too.
>
> Asserting that the refcount is at least 1 when entering
> pf_release_state() would express the same, but that’s also
> problematic.
> Of course, errors should trigger the KASSERT() in refcount_release(),
> so I think I may have convinced myself that the KASSERT() can in fact
> be removed and replaced with (void)refcount_release() and a comment
> explaining why this refcount_release() can never return 1.
>
So this:
diff --git a/sys/netpfil/pf/pf.c b/sys/netpfil/pf/pf.c
index 55ae1145835..0dbf1fe7f66 100644
--- a/sys/netpfil/pf/pf.c
+++ b/sys/netpfil/pf/pf.c
@@ -1623,7 +1623,6 @@ int
pf_unlink_state(struct pf_state *s, u_int flags)
{
struct pf_idhash *ih = &V_pf_idhash[PF_IDHASH(s)];
- int last;
if ((flags & PF_ENTER_LOCKED) == 0)
PF_HASHROW_LOCK(ih);
@@ -1664,8 +1663,9 @@ pf_unlink_state(struct pf_state *s, u_int flags)
PF_HASHROW_UNLOCK(ih);
pf_detach_state(s);
- last = refcount_release(&s->refs);
- KASSERT(last == 0, ("Incorrect state reference count"));
+ /* pf_state_insert() initialises refs to 2, so we can never
release the
+ * last reference here, only in pf_release_state(). */
+ (void)refcount_release(&s->refs);
return (pf_release_state(s));
}
I do assume that (void) will tell Coverity I’m deliberately ignoring
the return value. It’s a fairly common idiom, so I’d expect it to
understand.
Regards,
Kristof