Hi Chas,
On Thu, Sep 07, 2017 at 05:21:51PM -0400, Charles (Chas) Williams wrote:
> After commit 8f094a9ac5d7 ("mbuf: set mbuf fields while in pool") is it
> much harder to detect a "double free". If the developer makes a copy
> of an mbuf pointer and frees it twice, this condition is never detected
> and the mbuf gets returned to the pool twice.
>
> Since this requires extra work to track, make this behavior conditional
> on CONFIG_RTE_LIBRTE_MBUF_DEBUG.
>
> Signed-off-by: Chas Williams <ciwil...@brocade.com>
> ---
> lib/librte_mbuf/rte_mbuf.c | 2 +-
> lib/librte_mbuf/rte_mbuf.h | 40 ++++++++++++++++++++++++++++++++++------
> 2 files changed, 35 insertions(+), 7 deletions(-)
>
> diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
> index 26a62b8..b0d222c 100644
> --- a/lib/librte_mbuf/rte_mbuf.c
> +++ b/lib/librte_mbuf/rte_mbuf.c
> @@ -145,7 +145,7 @@ rte_pktmbuf_init(struct rte_mempool *mp,
> m->pool = mp;
> m->nb_segs = 1;
> m->port = 0xff;
> - rte_mbuf_refcnt_set(m, 1);
> + rte_mbuf_refcnt_set(m, RTE_MBUF_UNUSED_CNT);
> m->next = NULL;
> }
>
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index eaed7ee..1400b35 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -671,11 +671,15 @@ struct rte_pktmbuf_pool_private {
>
> #ifdef RTE_LIBRTE_MBUF_DEBUG
>
> +#define RTE_MBUF_UNUSED_CNT 0
> +
> /** check mbuf type in debug mode */
> #define __rte_mbuf_sanity_check(m, is_h) rte_mbuf_sanity_check(m, is_h)
>
> #else /* RTE_LIBRTE_MBUF_DEBUG */
>
> +#define RTE_MBUF_UNUSED_CNT 1
> +
> /** check mbuf type in debug mode */
> #define __rte_mbuf_sanity_check(m, is_h) do { } while (0)
>
> @@ -721,6 +725,9 @@ rte_mbuf_refcnt_set(struct rte_mbuf *m, uint16_t
> new_value)
> static inline uint16_t
> rte_mbuf_refcnt_update(struct rte_mbuf *m, int16_t value)
> {
> +#ifdef RTE_LIBRTE_MBUF_DEBUG
> + RTE_ASSERT(rte_mbuf_refcnt_read(m) != 0);
> +#endif
> /*
> * The atomic_add is an expensive operation, so we don't want to
> * call it in the case where we know we are the uniq holder of
> @@ -791,10 +798,9 @@ void
> rte_mbuf_sanity_check(const struct rte_mbuf *m, int is_header);
>
> #define MBUF_RAW_ALLOC_CHECK(m) do { \
> - RTE_ASSERT(rte_mbuf_refcnt_read(m) == 1); \
> + RTE_ASSERT(rte_mbuf_refcnt_read(m) == RTE_MBUF_UNUSED_CNT); \
> RTE_ASSERT((m)->next == NULL); \
> RTE_ASSERT((m)->nb_segs == 1); \
> - __rte_mbuf_sanity_check(m, 0); \
> } while (0)
>
> /**
> @@ -825,6 +831,10 @@ static inline struct rte_mbuf *rte_mbuf_raw_alloc(struct
> rte_mempool *mp)
> return NULL;
> m = (struct rte_mbuf *)mb;
> MBUF_RAW_ALLOC_CHECK(m);
> +#ifdef RTE_LIBRTE_MBUF_DEBUG
> + rte_mbuf_refcnt_set(m, 1);
> +#endif
> + __rte_mbuf_sanity_check(m, 0);
> return m;
> }
>
> @@ -846,10 +856,9 @@ static __rte_always_inline void
> rte_mbuf_raw_free(struct rte_mbuf *m)
> {
> RTE_ASSERT(RTE_MBUF_DIRECT(m));
> - RTE_ASSERT(rte_mbuf_refcnt_read(m) == 1);
> + RTE_ASSERT(rte_mbuf_refcnt_read(m) == RTE_MBUF_UNUSED_CNT);
> RTE_ASSERT(m->next == NULL);
> RTE_ASSERT(m->nb_segs == 1);
> - __rte_mbuf_sanity_check(m, 0);
> rte_mempool_put(m->pool, m);
> }
>
> @@ -1159,21 +1168,37 @@ static inline int rte_pktmbuf_alloc_bulk(struct
> rte_mempool *pool,
> case 0:
> while (idx != count) {
> MBUF_RAW_ALLOC_CHECK(mbufs[idx]);
> +#ifdef RTE_LIBRTE_MBUF_DEBUG
> + rte_mbuf_refcnt_set(mbufs[idx], 1);
> +#endif
> + __rte_mbuf_sanity_check(mbufs[idx], 0);
> rte_pktmbuf_reset(mbufs[idx]);
> idx++;
> /* fall-through */
> case 3:
> MBUF_RAW_ALLOC_CHECK(mbufs[idx]);
> +#ifdef RTE_LIBRTE_MBUF_DEBUG
> + rte_mbuf_refcnt_set(mbufs[idx], 1);
> +#endif
> + __rte_mbuf_sanity_check(mbufs[idx], 0);
> rte_pktmbuf_reset(mbufs[idx]);
> idx++;
> /* fall-through */
> case 2:
> MBUF_RAW_ALLOC_CHECK(mbufs[idx]);
> +#ifdef RTE_LIBRTE_MBUF_DEBUG
> + rte_mbuf_refcnt_set(mbufs[idx], 1);
> +#endif
> + __rte_mbuf_sanity_check(mbufs[idx], 0);
> rte_pktmbuf_reset(mbufs[idx]);
> idx++;
> /* fall-through */
> case 1:
> MBUF_RAW_ALLOC_CHECK(mbufs[idx]);
> +#ifdef RTE_LIBRTE_MBUF_DEBUG
> + rte_mbuf_refcnt_set(mbufs[idx], 1);
> +#endif
> + __rte_mbuf_sanity_check(mbufs[idx], 0);
> rte_pktmbuf_reset(mbufs[idx]);
> idx++;
> /* fall-through */
> @@ -1271,7 +1296,7 @@ static inline void rte_pktmbuf_detach(struct rte_mbuf
> *m)
> if (rte_mbuf_refcnt_update(md, -1) == 0) {
> md->next = NULL;
> md->nb_segs = 1;
> - rte_mbuf_refcnt_set(md, 1);
> + rte_mbuf_refcnt_set(md, RTE_MBUF_UNUSED_CNT);
> rte_mbuf_raw_free(md);
> }
> }
> @@ -1304,6 +1329,9 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> m->next = NULL;
> m->nb_segs = 1;
> }
> +#ifdef RTE_LIBRTE_MBUF_DEBUG
> + rte_mbuf_refcnt_set(m, RTE_MBUF_UNUSED_CNT);
> +#endif
>
> return m;
>
> @@ -1317,7 +1345,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> m->next = NULL;
> m->nb_segs = 1;
> }
> - rte_mbuf_refcnt_set(m, 1);
> + rte_mbuf_refcnt_set(m, RTE_MBUF_UNUSED_CNT);
>
> return m;
> }
> --
> 2.1.4
>
I'm afraid this won't work for drivers that use rte_mempool_get()
instead of rte_mbuf_raw_alloc(), because they will expect that
refcount is 1.
I didn't try, but an alternative to detect these double-frees
could be to enable RTE_LIBRTE_MEMPOOL_DEBUG. What do you think?
Olivier
