Date: Thu, 25 Jan 2018 15:31:02 -0800 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Kristof Provost <kp@FreeBSD.org> Cc: Ian Lepore <ian@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r328313 - head/sys/netpfil/pf Message-ID: <20180125233102.GN8113@FreeBSD.org> In-Reply-To: <14734657-ABC2-437B-9830-724901066342@FreeBSD.org> References: <201801240429.w0O4THIl059440@repo.freebsd.org> <20180125001310.GJ8113@FreeBSD.org> <1516840498.42536.213.camel@freebsd.org> <8FA39DD7-FD83-49D5-B7FC-3637B42129BE@FreeBSD.org> <14734657-ABC2-437B-9830-724901066342@FreeBSD.org>
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On Thu, Jan 25, 2018 at 02:46:14PM +1100, Kristof Provost wrote:
K> On 25 Jan 2018, at 12:08, Kristof Provost wrote:
K> > On 25 Jan 2018, at 11:34, Ian Lepore wrote:
K> >> On Wed, 2018-01-24 at 16:13 -0800, Gleb Smirnoff wrote:
K> >>> (r328313)
K> >>> K> @@ -1613,6 +1613,7 @@ int
K> >>> K> pf_unlink_state(struct pf_state *s, u_int flags)
K> >>> K> {
K> >>> K> struct pf_idhash *ih = &V_pf_idhash[PF_IDHASH(s)];
K> >>> K> + int last;
K> >>> K>
K> >>> K> if ((flags & PF_ENTER_LOCKED) == 0)
K> >>> K> PF_HASHROW_LOCK(ih);
K> >>> K> @@ -1653,7 +1654,8 @@ pf_unlink_state(struct pf_state *s, u_int
K> >>> flags)
K> >>> K> PF_HASHROW_UNLOCK(ih);
K> >>> K>
K> >>> K> pf_detach_state(s);
K> >>> K> - refcount_release(&s->refs);
K> >>> K> + last = refcount_release(&s->refs);
K> >>> K> + KASSERT(last == 0, ("Incorrect state reference count"));
K> >>> K>
K> >>> K> return (pf_release_state(s));
K> >>> K> }
K> >>>
K> >>> IMHO, we shouldn't emit extra code to please Coverity. We can mark
K> >>> it
K> >>> as a false positive in the interface. It may make sense to add a
K> >>> comment
K> >>> for a human to explain why return isn't checked here.
K> >>>
K> >>
K> >> Not to mention that when KASSERT compiles to nothing, what you're
K> >> left
K> >> with is a "defined but not used" warning for 'last'.
K> >>
K> > I’d really like to keep the KASSERT(), because this is the sort of
K> > thing that could go wrong, and the assertion would be helpful.
K> >
K> > I suppose I could wrap last in #ifdef INVARIANTS, but that’s rather
K> > ugly too.
K> >
K> > Asserting that the refcount is at least 1 when entering
K> > pf_release_state() would express the same, but that’s also
K> > problematic.
K> > Of course, errors should trigger the KASSERT() in refcount_release(),
K> > so I think I may have convinced myself that the KASSERT() can in fact
K> > be removed and replaced with (void)refcount_release() and a comment
K> > explaining why this refcount_release() can never return 1.
K> >
K> So this:
K>
K> diff --git a/sys/netpfil/pf/pf.c b/sys/netpfil/pf/pf.c
K> index 55ae1145835..0dbf1fe7f66 100644
K> --- a/sys/netpfil/pf/pf.c
K> +++ b/sys/netpfil/pf/pf.c
K> @@ -1623,7 +1623,6 @@ 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> @@ -1664,8 +1663,9 @@ pf_unlink_state(struct pf_state *s, u_int flags)
K> PF_HASHROW_UNLOCK(ih);
K>
K> pf_detach_state(s);
K> - last = refcount_release(&s->refs);
K> - KASSERT(last == 0, ("Incorrect state reference count"));
K> + /* pf_state_insert() initialises refs to 2, so we can never
K> release the
K> + * last reference here, only in pf_release_state(). */
K> + (void)refcount_release(&s->refs);
K>
K> return (pf_release_state(s));
K> }
K>
K> I do assume that (void) will tell Coverity I’m deliberately ignoring
K> the return value. It’s a fairly common idiom, so I’d expect it to
K> understand.
My vote goes for this one. A slightly better then warning when
compiling w/o INVARIANTS.
--
Gleb Smirnoff
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