Date: Wed, 21 Aug 2013 22:44:07 +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: <52152697.9070500@freebsd.org> In-Reply-To: <52151799.3020809@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> <52151368.40803@freebsd.org> <52151799.3020809@FreeBSD.org>
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On 21.08.2013 21:40, Navdeep Parhar wrote: > On 08/21/13 12:22, Andre Oppermann wrote: >> 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; >> + } > > The problem with this is that the mbuf may already be gone if it was > embedded in the cluster that was just freed by the ext free. That's why > skipmbuf is used to cache the M_NOFREE bit. Next try: ;) Index: kern/uipc_mbuf.c =================================================================== --- kern/uipc_mbuf.c (revision 254605) +++ kern/uipc_mbuf.c (working copy) @@ -284,9 +284,12 @@ KASSERT(m->m_ext.ref_cnt != NULL, ("%s: ref_cnt not set", __func__)); /* - * check if the header is embedded in the cluster + * Do not free if the mbuf is embedded in the cluster + * but make sure to get rid of any tag chains first. */ skipmbuf = (m->m_flags & M_NOFREE); + if (skipmbuf && (m->m_flags & M_PKTHDR)) + m_tag_delete_chain(m, NULL); /* Free attached storage if this mbuf is the only reference to it. */ if (*(m->m_ext.ref_cnt) == 1 || -- Andre
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