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) ) {
+ /* 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;
+ }
- 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;
}
/**
