RE: [PATCH] lib/mempool : rte_mempool_avail_count, fixing return bigger than mempool size

["Morten Brørup" <mb@smartsharesystems.com>]

> From: David Marchand [mailto:david.marchand@redhat.com]
> Sent: Wednesday, 17 May 2023 13.53
> 
> On Wed, May 17, 2023 at 11:05 AM Morten Brørup <mb@smartsharesystems.com>
> wrote:
> > > On Tue, 16 May 2023 13:41:46 +0000
> > > Yasin CANER <yasinncaner@gmail.com> wrote:
> > >
> > > > From: Yasin CANER <yasin.caner@ulakhaberlesme.com.tr>
> > > >
> > > > after a while working rte_mempool_avail_count function returns bigger
> > > > than mempool size that cause miscalculation rte_mempool_in_use_count.
> > > >
> > > > it helps to avoid miscalculation rte_mempool_in_use_count.
> 
> Is this issue reproduced with an application of the reporter, or a
> DPDK in-tree application?
> 
> 
> > > >
> > > > Bugzilla ID: 1229
> > > >
> > > > Signed-off-by: Yasin CANER <yasin.caner@ulakhaberlesme.com.tr>
> > >
> > > An alternative that avoids some code duplication.
> > >
> > > diff --git a/lib/mempool/rte_mempool.c b/lib/mempool/rte_mempool.c
> > > index cf5dea2304a7..2406b112e7b0 100644
> > > --- a/lib/mempool/rte_mempool.c
> > > +++ b/lib/mempool/rte_mempool.c
> > > @@ -1010,7 +1010,7 @@ rte_mempool_avail_count(const struct rte_mempool
> > > *mp)
> > >         count = rte_mempool_ops_get_count(mp);
> > >
> > >         if (mp->cache_size == 0)
> > > -               return count;
> > > +               goto exit;
> >
> > This bug can only occur here (i.e. with cache_size==0) if
> rte_mempool_ops_get_count() returns an incorrect value. The bug should be
> fixed there instead.
> >
> >
> >
> > MB (continued): The bug must be in the underlying mempool driver. I took a
> look at the ring and stack drivers, and they seem fine.
> 
> Or it could indicate a double free (or equivalent) issue from the
> application (either through direct call to mempool API, or indirectly
> like sending/freeing an already sent/freed packet for example).

Good point, David.

@Yasin, if you build DPDK and your application with RTE_LIBRTE_MEMPOOL_DEBUG set in config/rte_config.h, the mempool cookies should catch any double frees.