From 1f132ff145cee99959db38a8630abd8a84b99f3e Mon Sep 17 00:00:00 2001 From: Mark Johnston Date: Fri, 2 Aug 2024 13:09:41 +0000 Subject: [PATCH] xen/netfront: Decouple XENNET tags from mbuf lifetimes netmap's generic mode tries to improve performance by minimizing mbuf allocations. In service of this goal, it maintains an extra reference to the mbuf and polls the counter to see if the driver has released its reference by calling m_freem(). As a result, the extref destructor is not called when expected by the netfront driver, and mbufs tags are not freed. Modify the tx path to release its mbuf tags promptly when reclaiming tx descriptors. They are drawn from a fixed-size pool, so otherwise are quickly exhausted when a netfront interface is in netmap generic mode. Co-authored by: royger MFC after: 2 weeks Fixes: dabb3db7a817 ("xen/netfront: deal with mbuf data crossing a page boundary") Sponsored by: Cloud Software Group Sponsored by: Klara, Inc. Sponsored by: Zenarmor --- sys/dev/xen/netfront/netfront.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/sys/dev/xen/netfront/netfront.c b/sys/dev/xen/netfront/netfront.c index 6ac6ecc3bdb..e13fb8765ba 100644 --- a/sys/dev/xen/netfront/netfront.c +++ b/sys/dev/xen/netfront/netfront.c @@ -335,8 +335,16 @@ static void mbuf_release(struct mbuf *m) KASSERT(ref != NULL, ("Cannot find refcount")); KASSERT(ref->count > 0, ("Invalid reference count")); - if (--ref->count == 0) + if (--ref->count == 0) { + /* + * Explicitly free the tag while we hold the tx queue lock. + * This ensures that the tag is deleted promptly in case + * something else is holding extra references to the mbuf chain, + * such as netmap. + */ + m_tag_delete(m, &ref->tag); m_freem(m); + } } static void tag_free(struct m_tag *t)