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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