Date: Thu, 9 Sep 2004 21:46:00 +0100 From: Brian Somers <brian@Awfulhak.org> To: freebsd-net@FreeBSD.org Subject: uma_zcreate() call from kern_mbuf.c - bug? Message-ID: <20040909214600.12bb5fd5@dev.lan.Awfulhak.org>
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I'm a bit confused by this uma_zcreate() call in kern_mbuf.c:
zone_mbuf = uma_zcreate("Mbuf", MSIZE, mb_ctor_mbuf, mb_dtor_mbuf,
NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_MAXBUCKET);
Given that dtom() is defined as:
#define dtom(x) ((struct mbuf *)((intptr_t)(x) & ~(MSIZE-1)))
shouldn't this mean that the uma_zcreate should be:
zone_mbuf = uma_zcreate("Mbuf", MSIZE, mb_ctor_mbuf, mb_dtor_mbuf,
NULL, NULL, MSIZE - 1, UMA_ZONE_MAXBUCKET);
Of course m_get() et. al. seem to manage to get MSIZE aligned pointers back
from uma_zalloc_arg(zone_mbuf...) anyway, but surely that's an implementation
side effect and the align argument should be corrected.
There should probably also be a KASSERT here to ensure that MSIZE is sane (and
to stop idiots like me from shooting themselves in the foot with ``options
MSIZE=320'').
Comments on this patch ?
Index: kern_mbuf.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/kern_mbuf.c,v
retrieving revision 1.3
diff -u -r1.3 kern_mbuf.c
--- kern_mbuf.c 2 Aug 2004 00:18:35 -0000 1.3
+++ kern_mbuf.c 9 Sep 2004 20:24:46 -0000
@@ -131,11 +131,15 @@
mbuf_init(void *dummy)
{
+ /* Ensure that MSIZE doesn't break dtom() */
+ KASSERT((((MSIZE - 1) ^ MSIZE) + 1) >> 1 == MSIZE,
+ ("Invalid MSIZE - must only have a single bit set"));
+
/*
* Configure UMA zones for Mbufs, Clusters, and Packets.
*/
zone_mbuf = uma_zcreate("Mbuf", MSIZE, mb_ctor_mbuf, mb_dtor_mbuf,
- NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_MAXBUCKET);
+ NULL, NULL, MSIZE - 1, UMA_ZONE_MAXBUCKET);
zone_clust = uma_zcreate("MbufClust", MCLBYTES, mb_ctor_clust,
mb_dtor_clust, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_REFCNT);
if (nmbclusters > 0)
--
Brian <brian@Awfulhak.org> <brian@[uk.]FreeBSD.org>
<http://www.Awfulhak.org>; <brian@[uk.]OpenBSD.org>
Don't _EVER_ lose your sense of humour !
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