>
> On Tue, Mar 18, 2014 at 09:45:14PM -0400, Stefan Berger wrote:
> > From: Stefan Berger <stefanb@xxxxxxxxxxxxxxxxxx>
> >
> > https://bugzilla.redhat.com/show_bug.cgi?id=1071181
> >
> > Commit 49b59a15 fixed one problem but masks another one related to pointer
> > freeing.
> >
> > Use virAtomicIntGet() to test for 0 rather than trying to test for 'true'
> > after virAtomicIntDecAndTest().
> >
> > Avoid putting of the virNWFilterSnoopReq once the thread has been started.
> >
> > Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxxxxxxx>
> > ---
> > src/nwfilter/nwfilter_dhcpsnoop.c | 11 +++++++++--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/nwfilter/nwfilter_dhcpsnoop.c b/src/nwfilter/
> nwfilter_dhcpsnoop.c
> > index d2a8062..32ca304 100644
> > --- a/src/nwfilter/nwfilter_dhcpsnoop.c
> > +++ b/src/nwfilter/nwfilter_dhcpsnoop.c
> > @@ -720,7 +720,10 @@ virNWFilterSnoopReqPut(virNWFilterSnoopReqPtr req)
> >
> > virNWFilterSnoopLock();
> >
> > - if (virAtomicIntDecAndTest(&req->refctr)) {
> > + virAtomicIntDecAndTest(&req->refctr);
> > +
> > + /* make sure it's 0; virAtomitIntDecAndTest may return true on '1' */
> > + if (virAtomicIntGet(&req->refctr) == 0) {
>
> NACK, using two atomic functions, you are making this non-atomic.
> between these two atomic operations many things can happen an it's not
> what you want I bet. The virAtomicIntDecAndTest() uses
> __sync_fetch_and_sub(atomic, 1) and compares it to 1, that's true, but
> since it is fetch_and_sub (and not the other way around, the value
> being compared to 1 is the value that the atomic had before it was
> decremented. That means it returns 1 (true) if and only if the
> current value is 0. virAtomicIntDecAndTest() is what you really want
> and should use here.
Right. I initially thought there was something wrong in this part here until I found the double free error is related to the other part. So this part you comment on doesn't need to be changed.
Stefan
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