Date: Wed, 21 Aug 2013 21:22:16 +0200 From: Andre Oppermann <andre@freebsd.org> To: Navdeep Parhar <np@FreeBSD.org> Cc: svn-src-head@freebsd.org, freebsd-net@freebsd.org, Peter Grehan <grehan@freebsd.org> Subject: Re: M_NOFREE removal (was Re: svn commit: r254520 - in head/sys: kern sys) Message-ID: <52151368.40803@freebsd.org> In-Reply-To: <521505A3.4020103@FreeBSD.org> References: <201308191116.r7JBGsc6065793@svn.freebsd.org> <521256CE.6070706@FreeBSD.org> <5212587A.2080202@freebsd.org> <52128937.1010407@freebsd.org> <52129E55.30803@freebsd.org> <5214D7E8.1080106@freebsd.org> <5214ED19.40907@FreeBSD.org> <5215047C.8080107@freebsd.org> <521505A3.4020103@FreeBSD.org>
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On 21.08.2013 20:23, Navdeep Parhar wrote:
> I believe we need an extra patch to get M_NOFREE correct. I've had it
> forever in some of my internal repos but never committed it upstream
> (just plain forgot). Since this stuff is fresh in your mind, can you
> review this:
>
> diff -r cd78031b7885 sys/sys/mbuf.h
> --- a/sys/sys/mbuf.h Fri Aug 16 13:35:26 2013 -0700
> +++ b/sys/sys/mbuf.h Wed Aug 21 10:55:57 2013 -0700
> @@ -535,6 +535,8 @@ m_free(struct mbuf *m)
> {
> struct mbuf *n = m->m_next;
>
> + if ((m->m_flags & (M_PKTHDR|M_NOFREE)) == (M_PKTHDR|M_NOFREE))
> + m_tag_delete_chain(m, NULL);
> if (m->m_flags & M_EXT)
> mb_free_ext(m);
> else if ((m->m_flags & M_NOFREE) == 0)
>
> It prevents leaks of tags from M_NOFREE+pkthdr mbufs.
Good point. Looks correct.
But then I wonder if it is really a smart thing to allow single
mbufs (w/o M_EXT) to be M_NOFREE at the same time. They easily
get lost. If it doesn't have an external buffer attached there
is no way to know when and if it was freed.
If M_NOFREE is only allowed together with M_EXT then the tag chain
delete should happen in mb_ext_free() next to 'skipmbuf' instead.
Index: kern/uipc_mbuf.c
===================================================================
--- kern/uipc_mbuf.c (revision 254605)
+++ kern/uipc_mbuf.c (working copy)
@@ -283,11 +283,6 @@
KASSERT((m->m_flags & M_EXT) == M_EXT, ("%s: M_EXT not set", __func__));
KASSERT(m->m_ext.ref_cnt != NULL, ("%s: ref_cnt not set", __func__));
- /*
- * check if the header is embedded in the cluster
- */
- skipmbuf = (m->m_flags & M_NOFREE);
-
/* Free attached storage if this mbuf is the only reference to it. */
if (*(m->m_ext.ref_cnt) == 1 ||
atomic_fetchadd_int(m->m_ext.ref_cnt, -1) == 1) {
@@ -328,8 +323,14 @@
("%s: unknown ext_type", __func__));
}
}
- if (skipmbuf)
+
+ /*
+ * Do not free if the mbuf is embedded in the cluster.
+ */
+ if (m->m_flags & M_NOFREE) {
+ m_tag_delete_chain(m, NULL);
return;
+ }
/*
* Free this mbuf back to the mbuf zone with all m_ext
--
Andre
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