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From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Hiroyuki Mikita <h.mikita89@gmail.com>, "olivier.matz@6wind.com"
<olivier.matz@6wind.com>
CC: "dev@dpdk.org" <dev@dpdk.org>
Thread-Topic: [dpdk-dev] [PATCH v2] mbuf: decrease refcnt when detaching
Thread-Index: AQHRr5OGTZbJUl8op0mwi7XajqfNVp+892Eg
Date: Tue, 17 May 2016 11:06:27 +0000
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Subject: Re: [dpdk-dev] [PATCH v2] mbuf: decrease refcnt when detaching
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Hi Hiroyuki,
>=20
> The rte_pktmbuf_detach() function should decrease refcnt on a direct
> buffer.
>=20
> 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_det=
ach().
> * checked refcnt when detaching in unit tests.
> * added this issue to release notes.
>=20
> 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(-)
>=20
> 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 =3D NULL;
> struct rte_mbuf *clone2 =3D NULL;
> char *data, *c_data, *c_data2;
> + uint16_t refcnt;
>=20
> /* alloc a mbuf */
> m =3D rte_pktmbuf_alloc(pktmbuf_pool);
> @@ -508,13 +509,17 @@ test_attach_from_different_pool(void)
> GOTO_FAIL("invalid refcnt in m\n");
>=20
> /* detach the clones */
> - rte_pktmbuf_detach(clone);
> + refcnt =3D rte_pktmbuf_detach2(clone);
> if (c_data !=3D rte_pktmbuf_mtod(clone, char *))
> GOTO_FAIL("clone was not detached properly\n");
> + if (refcnt !=3D 2 || rte_mbuf_refcnt_read(m) !=3D 2)
> + GOTO_FAIL("invalid refcnt in m\n");
>=20
> - rte_pktmbuf_detach(clone2);
> + refcnt =3D rte_pktmbuf_detach2(clone2);
> if (c_data2 !=3D rte_pktmbuf_mtod(clone2, char *))
> GOTO_FAIL("clone2 was not detached properly\n");
> + if (refcnt !=3D 1 || rte_mbuf_refcnt_read(m) !=3D 1)
> + GOTO_FAIL("invalid refcnt in m\n");
>=20
> /* 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_note=
s/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
> ------------
>=20
> -This section should contain new known issues in this release. Sample for=
mat:
> -
> -* **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()``.
>=20
> 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 =3D m->pool;
> + uint32_t mbuf_size, buf_len, priv_size;
> +
> + priv_size =3D rte_pktmbuf_priv_size(mp);
> + mbuf_size =3D sizeof(struct rte_mbuf) + priv_size;
> + buf_len =3D rte_pktmbuf_data_room_size(mp);
> +
> + m->priv_size =3D priv_size;
> + m->buf_addr =3D (char *)m + mbuf_size;
> + m->buf_physaddr =3D rte_mempool_virt2phy(mp, m) + mbuf_size;
> + m->buf_len =3D (uint16_t)buf_len;
> + m->data_off =3D RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
> + m->data_len =3D 0;
> + m->ol_flags =3D 0;
> +}
I still think it would be good to have a separate function for what rte_pkt=
mbuf_detach()
Is doing right now: restore original values of indirect mbuf.
Probably rename it to rte_pktmbuf_restore() or so and make _detach2() (unat=
ach() ?)
to call it internally.=20
> +
> +/**
> + * 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 =3D rte_mbuf_from_indirect(m);
> struct rte_mempool *mp =3D m->pool;
> uint32_t mbuf_size, buf_len, priv_size;
>=20
> @@ -1482,6 +1518,8 @@ static inline void rte_pktmbuf_detach(struct rte_mb=
uf *m)
> m->data_off =3D RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
> m->data_len =3D 0;
> m->ol_flags =3D 0;
> +
> + return rte_mbuf_refcnt_update(md, -1);
> }
>=20
> 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 =3D rte_mbuf_from_indirect(m);
I don't think there is a need to invoke rte_mbuf_from_indirect() twice.
You can either pass md as a second parameter to _detach2(),
or make detach2() to invoke __rte_mbuf_raw_free()
if rte_mbuf_refcnt_update(md, -1) =3D=3D 0.
Konstantin
> - rte_pktmbuf_detach(m);
> - if (rte_mbuf_refcnt_update(md, -1) =3D=3D 0)
> + if (rte_pktmbuf_detach2(m) =3D=3D 0)
> __rte_mbuf_raw_free(md);
> }
> return m;
> --
> 1.9.1