mbuf: fix reset on mbuf free

m->nb_seg must be reset on mbuf free whatever the value of m->next,
because it can happen that m->nb_seg is != 1. For instance in this
case:

  m1 = rte_pktmbuf_alloc(mp);
  rte_pktmbuf_append(m1, 500);
  m2 = rte_pktmbuf_alloc(mp);
  rte_pktmbuf_append(m2, 500);
  rte_pktmbuf_chain(m1, m2);
  m0 = rte_pktmbuf_alloc(mp);
  rte_pktmbuf_append(m0, 500);
  rte_pktmbuf_chain(m0, m1);

As rte_pktmbuf_chain() does not reset nb_seg in the initial m1
segment (this is not required), after this code the mbuf chain
have 3 segments:
  - m0: next=m1, nb_seg=3
  - m1: next=m2, nb_seg=2
  - m2: next=NULL, nb_seg=1

Then split this chain between m1 and m2, it would result in 2 packets:
  - first packet
    - m0: next=m1, nb_seg=2
    - m1: next=NULL, nb_seg=2
  - second packet
    - m2: next=NULL, nb_seg=1

Freeing the first packet will not restore nb_seg=1 in the second
segment. This is an issue because it is expected that mbufs stored
in pool have their nb_seg field set to 1.

Fixes: 8f094a9ac5d7 ("mbuf: set mbuf fields while in pool")
Cc: stable@dpdk.org
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

diff --git a/app/test/test_mbuf.c b/app/test/test_mbuf.c
index a40f7d4..ad2cbab 100644 (file)
--- a/app/test/test_mbuf.c
+++ b/app/test/test_mbuf.c
@@ -2677,6 +2677,70 @@ fail:
        return -1;
 }
 
+/* check that m->nb_segs and m->next are reset on mbuf free */
+static int
+test_nb_segs_and_next_reset(void)
+{
+       struct rte_mbuf *m0 = NULL, *m1 = NULL, *m2 = NULL;
+       struct rte_mempool *pool = NULL;
+
+       pool = rte_pktmbuf_pool_create("test_mbuf_reset",
+                       3, 0, 0, MBUF_DATA_SIZE, SOCKET_ID_ANY);
+       if (pool == NULL)
+               GOTO_FAIL("Failed to create mbuf pool");
+
+       /* alloc mbufs */
+       m0 = rte_pktmbuf_alloc(pool);
+       m1 = rte_pktmbuf_alloc(pool);
+       m2 = rte_pktmbuf_alloc(pool);
+       if (m0 == NULL || m1 == NULL || m2 == NULL)
+               GOTO_FAIL("Failed to allocate mbuf");
+
+       /* append data in all of them */
+       if (rte_pktmbuf_append(m0, 500) == NULL ||
+                       rte_pktmbuf_append(m1, 500) == NULL ||
+                       rte_pktmbuf_append(m2, 500) == NULL)
+               GOTO_FAIL("Failed to append data in mbuf");
+
+       /* chain them in one mbuf m0 */
+       rte_pktmbuf_chain(m1, m2);
+       rte_pktmbuf_chain(m0, m1);
+       if (m0->nb_segs != 3 || m0->next != m1 || m1->next != m2 ||
+                       m2->next != NULL) {
+               m1 = m2 = NULL;
+               GOTO_FAIL("Failed to chain mbufs");
+       }
+
+       /* split m0 chain in two, between m1 and m2 */
+       m0->nb_segs = 2;
+       m1->next = NULL;
+       m2->nb_segs = 1;
+
+       /* free the 2 mbuf chains m0 and m2  */
+       rte_pktmbuf_free(m0);
+       rte_pktmbuf_free(m2);
+
+       /* realloc the 3 mbufs */
+       m0 = rte_mbuf_raw_alloc(pool);
+       m1 = rte_mbuf_raw_alloc(pool);
+       m2 = rte_mbuf_raw_alloc(pool);
+       if (m0 == NULL || m1 == NULL || m2 == NULL)
+               GOTO_FAIL("Failed to reallocate mbuf");
+
+       /* ensure that m->next and m->nb_segs are reset allocated mbufs */
+       if (m0->nb_segs != 1 || m0->next != NULL ||
+                       m1->nb_segs != 1 || m1->next != NULL ||
+                       m2->nb_segs != 1 || m2->next != NULL)
+               GOTO_FAIL("nb_segs or next was not reset properly");
+
+       return 0;
+
+fail:
+       if (pool != NULL)
+               rte_mempool_free(pool);
+       return -1;
+}
+
 static int
 test_mbuf(void)
 {
@@ -2867,6 +2931,11 @@ test_mbuf(void)
                goto err;
        }
 
+       /* test reset of m->nb_segs and m->next on mbuf free */
+       if (test_nb_segs_and_next_reset() < 0) {
+               printf("test_nb_segs_and_next_reset() failed\n");
+               goto err;
+       }
 
        ret = 0;
 err:

diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
index 7d09ee2..5f77840 100644 (file)
--- a/lib/librte_mbuf/rte_mbuf.c
+++ b/lib/librte_mbuf/rte_mbuf.c
@@ -129,10 +129,10 @@ rte_pktmbuf_free_pinned_extmem(void *addr, void *opaque)
 
        rte_mbuf_ext_refcnt_set(m->shinfo, 1);
        m->ol_flags = EXT_ATTACHED_MBUF;
-       if (m->next != NULL) {
+       if (m->next != NULL)
                m->next = NULL;
+       if (m->nb_segs != 1)
                m->nb_segs = 1;
-       }
        rte_mbuf_raw_free(m);
 }
 

diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index c4c9ebf..8c1097e 100644 (file)
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -1340,10 +1340,10 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
                                return NULL;
                }
 
-               if (m->next != NULL) {
+               if (m->next != NULL)
                        m->next = NULL;
+               if (m->nb_segs != 1)
                        m->nb_segs = 1;
-               }
 
                return m;
 
@@ -1357,10 +1357,10 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
                                return NULL;
                }
 
-               if (m->next != NULL) {
+               if (m->next != NULL)
                        m->next = NULL;
+               if (m->nb_segs != 1)
                        m->nb_segs = 1;
-               }
                rte_mbuf_refcnt_set(m, 1);
 
                return m;

diff --git a/lib/librte_mbuf/rte_mbuf_core.h b/lib/librte_mbuf/rte_mbuf_core.h
index 567551d..78a1fcc 100644 (file)
--- a/lib/librte_mbuf/rte_mbuf_core.h
+++ b/lib/librte_mbuf/rte_mbuf_core.h
@@ -495,7 +495,12 @@ struct rte_mbuf {
         * or non-atomic) is controlled by the RTE_MBUF_REFCNT_ATOMIC flag.
         */
        uint16_t refcnt;
-       uint16_t nb_segs;         /**< Number of segments. */
+
+       /**
+        * Number of segments. Only valid for the first segment of an mbuf
+        * chain.
+        */
+       uint16_t nb_segs;
 
        /** Input port (16 bits to support more than 256 virtual ports).
         * The event eth Tx adapter uses this field to specify the output port.
@@ -591,7 +596,11 @@ struct rte_mbuf {
        /* second cache line - fields only used in slow path or on TX */
        RTE_MARKER cacheline1 __rte_cache_min_aligned;
 
-       struct rte_mbuf *next;    /**< Next segment of scattered packet. */
+       /**
+        * Next segment of scattered packet. Must be NULL in the last segment or
+        * in case of non-segmented packet.
+        */
+       struct rte_mbuf *next;
 
        /* fields to support TX offloads */
        RTE_STD_C11