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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