[dpdk-dev] [PATCH v3] mbuf: use refcnt = 0 when debugging

[Charles (Chas) Williams]

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 <ciwillia at 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