[dpdk-dev] [PATCH v2] mbuf: decrease refcnt when detaching

[Hiroyuki Mikita <h.mikita89@gmail.com>]

The rte_pktmbuf_detach() function should decrease refcnt on a direct
buffer.

Signed-off-by: Hiroyuki Mikita <h.mikita89@gmail.com>
---
v2:
* introduced a new function rte_pktmbuf_detach2() which decrease refcnt.
* marked rte_pktmbuf_detach() as deprecated.
* added comments about refcnt to rte_pktmbuf_attach() and rte_pktmbuf_detach().
* checked refcnt when detaching in unit tests.
* added this issue to release notes.

 app/test/test_mbuf.c                   |  9 +++++--
 doc/guides/rel_notes/release_16_07.rst | 11 ++++-----
 lib/librte_mbuf/rte_mbuf.h             | 43 +++++++++++++++++++++++++++++++---
 3 files changed, 51 insertions(+), 12 deletions(-)

diff --git a/app/test/test_mbuf.c b/app/test/test_mbuf.c
index 98ff93a..2bf05eb 100644
--- a/app/test/test_mbuf.c
+++ b/app/test/test_mbuf.c
@@ -438,6 +438,7 @@ test_attach_from_different_pool(void)
 	struct rte_mbuf *clone = NULL;
 	struct rte_mbuf *clone2 = NULL;
 	char *data, *c_data, *c_data2;
+	uint16_t refcnt;
 
 	/* alloc a mbuf */
 	m = rte_pktmbuf_alloc(pktmbuf_pool);
@@ -508,13 +509,17 @@ test_attach_from_different_pool(void)
 		GOTO_FAIL("invalid refcnt in m\n");
 
 	/* detach the clones */
-	rte_pktmbuf_detach(clone);
+	refcnt = rte_pktmbuf_detach2(clone);
 	if (c_data != rte_pktmbuf_mtod(clone, char *))
 		GOTO_FAIL("clone was not detached properly\n");
+	if (refcnt != 2 || rte_mbuf_refcnt_read(m) != 2)
+		GOTO_FAIL("invalid refcnt in m\n");
 
-	rte_pktmbuf_detach(clone2);
+	refcnt = rte_pktmbuf_detach2(clone2);
 	if (c_data2 != rte_pktmbuf_mtod(clone2, char *))
 		GOTO_FAIL("clone2 was not detached properly\n");
+	if (refcnt != 1 || rte_mbuf_refcnt_read(m) != 1)
+		GOTO_FAIL("invalid refcnt in m\n");
 
 	/* free the clones and the initial mbuf */
 	rte_pktmbuf_free(clone2);
diff --git a/doc/guides/rel_notes/release_16_07.rst b/doc/guides/rel_notes/release_16_07.rst
index f6d543c..9678c1f 100644
--- a/doc/guides/rel_notes/release_16_07.rst
+++ b/doc/guides/rel_notes/release_16_07.rst
@@ -77,13 +77,10 @@ Other
 Known Issues
 ------------
 
-This section should contain new known issues in this release. Sample format:
-
-* **Add title in present tense with full stop.**
-
-  Add a short 1-2 sentence description of the known issue in the present
-  tense. Add information on any known workarounds.
-
+* The ``rte_pktmbuf_detach()`` function does not decrement the direct
+  mbuf's reference counter. It leads a memory leak of the direct
+  mbuf. The workaround is to explicitly decrement the reference
+  counter or use ``rte_pktmbuf_detach2()``.
 
 API Changes
 -----------
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 529debb..c0a592d 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -1408,6 +1408,7 @@ static inline int rte_pktmbuf_alloc_bulk(struct rte_mempool *pool,
  *
  * After attachment we refer the mbuf we attached as 'indirect',
  * while mbuf we attached to as 'direct'.
+ * The direct mbuf's reference counter is incremented.
  * Right now, not supported:
  *  - attachment for already indirect mbuf (e.g. - mi has to be direct).
  *  - mbuf we trying to attach (mi) is used by someone else
@@ -1459,15 +1460,50 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *m)
 /**
  * Detach an indirect packet mbuf.
  *
+ * Note: It is deprecated.
+ * The direct mbuf's reference counter is not decremented.
+ *
+ *  - restore original mbuf address and length values.
+ *  - reset pktmbuf data and data_len to their default values.
+ *  All other fields of the given packet mbuf will be left intact.
+ *
+ * @param m
+ *   The indirect attached packet mbuf.
+ */
+static inline void __rte_deprecated rte_pktmbuf_detach(struct rte_mbuf *m)
+{
+	struct rte_mempool *mp = m->pool;
+	uint32_t mbuf_size, buf_len, priv_size;
+
+	priv_size = rte_pktmbuf_priv_size(mp);
+	mbuf_size = sizeof(struct rte_mbuf) + priv_size;
+	buf_len = rte_pktmbuf_data_room_size(mp);
+
+	m->priv_size = priv_size;
+	m->buf_addr = (char *)m + mbuf_size;
+	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + mbuf_size;
+	m->buf_len = (uint16_t)buf_len;
+	m->data_off = RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
+	m->data_len = 0;
+	m->ol_flags = 0;
+}
+
+/**
+ * Detach an indirect packet mbuf.
+ *
  *  - restore original mbuf address and length values.
  *  - reset pktmbuf data and data_len to their default values.
  *  All other fields of the given packet mbuf will be left intact.
+ *  - decrement the direct mbuf's reference counter.
  *
  * @param m
  *   The indirect attached packet mbuf.
+ * @return
+ *   The updated value of the direct mbuf's reference counter.
  */
-static inline void rte_pktmbuf_detach(struct rte_mbuf *m)
+static inline uint16_t rte_pktmbuf_detach2(struct rte_mbuf *m)
 {
+	struct rte_mbuf *md = rte_mbuf_from_indirect(m);
 	struct rte_mempool *mp = m->pool;
 	uint32_t mbuf_size, buf_len, priv_size;
 
@@ -1482,6 +1518,8 @@ static inline void rte_pktmbuf_detach(struct rte_mbuf *m)
 	m->data_off = RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
 	m->data_len = 0;
 	m->ol_flags = 0;
+
+	return rte_mbuf_refcnt_update(md, -1);
 }
 
 static inline struct rte_mbuf* __attribute__((always_inline))
@@ -1497,8 +1535,7 @@ __rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
 		 */
 		if (RTE_MBUF_INDIRECT(m)) {
 			struct rte_mbuf *md = rte_mbuf_from_indirect(m);
-			rte_pktmbuf_detach(m);
-			if (rte_mbuf_refcnt_update(md, -1) == 0)
+			if (rte_pktmbuf_detach2(m) == 0)
 				__rte_mbuf_raw_free(md);
 		}
 		return m;
-- 
1.9.1