On Tue, Dec 05, 2023 at 10:50:32AM -0800, Stephen Hemminger wrote:
> On Mon, 4 Dec 2023 11:07:08 +0000
> Konstantin Ananyev <konstantin.anan...@huawei.com> wrote:
>
> > > > 2.25.1
> > >
> > > NAK.
> > >
> > > This patch is not race safe.
> >
> > +1, It is a bad idea.
>
> The patch does raise a couple of issues that could be addressed by
> rearranging. There is duplicate code, and there are no comments
> to explain the rationale.
>
> Maybe something like the following (untested):
>
> diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h
> index 286b32b788a5..b43c055fbe3f 100644
> --- a/lib/mbuf/rte_mbuf.h
> +++ b/lib/mbuf/rte_mbuf.h
> @@ -1342,42 +1342,32 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> {
> __rte_mbuf_sanity_check(m, 0);
>
> - if (likely(rte_mbuf_refcnt_read(m) == 1)) {
> -
> - if (!RTE_MBUF_DIRECT(m)) {
> - rte_pktmbuf_detach(m);
> - if (RTE_MBUF_HAS_EXTBUF(m) &&
> - RTE_MBUF_HAS_PINNED_EXTBUF(m) &&
> - __rte_pktmbuf_pinned_extbuf_decref(m))
> - return NULL;
> - }
> -
> - if (m->next != NULL)
> - m->next = NULL;
> - if (m->nb_segs != 1)
> - m->nb_segs = 1;
> -
> - return m;
> -
> - } else if (__rte_mbuf_refcnt_update(m, -1) == 0) {
> -
> - if (!RTE_MBUF_DIRECT(m)) {
> - rte_pktmbuf_detach(m);
> - if (RTE_MBUF_HAS_EXTBUF(m) &&
> - RTE_MBUF_HAS_PINNED_EXTBUF(m) &&
> - __rte_pktmbuf_pinned_extbuf_decref(m))
> - return NULL;
> - }
> -
> - if (m->next != NULL)
> - m->next = NULL;
> - if (m->nb_segs != 1)
> - m->nb_segs = 1;
> + if (likely(rte_mbuf_refcnt_read(m) != 1) ) {
== 1
> + /* If this is the only reference to the mbuf it can just
> + * be setup for reuse without modifying reference count.
> + */
> + } else if (unlikely(__rte_mbuf_refcnt_update(m, -1) == 0)) {
> + /* This was last reference reset to 1 for recycling/free. */
> rte_mbuf_refcnt_set(m, 1);
> + } else {
> + /* mbuf is still in use */
> + return NULL;
> + }
>
This seems much clearer with good comments.
> - return m;
> + if (!RTE_MBUF_DIRECT(m)) {
> + rte_pktmbuf_detach(m);
> + if (RTE_MBUF_HAS_EXTBUF(m) &&
> + RTE_MBUF_HAS_PINNED_EXTBUF(m) &&
> + __rte_pktmbuf_pinned_extbuf_decref(m))
> +
> + return NULL;
> }
> - return NULL;
> +
> + if (m->next != NULL)
> + m->next = NULL;
> + if (m->nb_segs != 1)
> + m->nb_segs = 1;
> + return m;
> }
>
> /**
