Date: Tue, 28 Aug 2012 21:24:08 -0600 From: Warner Losh <imp@bsdimp.com> To: Adrian Chadd <adrian@freebsd.org> Cc: scottl@freebsd.org, freebsd-mips@freebsd.org Subject: Re: MIPS busdma map questions Message-ID: <1F780BF4-84C3-48D5-9832-EA32381969A6@bsdimp.com> In-Reply-To: <CAJ-VmomuwKKaQ6AszeDo-iQwL%2B8DPJpBB9av0K%2BVbaj2feHO7g@mail.gmail.com> References: <CAJ-VmomuwKKaQ6AszeDo-iQwL%2B8DPJpBB9av0K%2BVbaj2feHO7g@mail.gmail.com>
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On Aug 28, 2012, at 8:22 PM, Adrian Chadd wrote: > Hi, > > I have a couple of busdma map questions. > > #1 - in mips/mips/busdma_machdep.c, bus_dmamap_destroy() calls > _busdma_free_dmamap() and -then- goes and walks the dma map list. Is > this a good idea or not? :) Accessing free memory after freeing it is a free ticket to a free dose of free pain. It should be freed after the if that checks to see if it is in use. > #2 - the ath(4) code (in sys/dev/ath/if_ath.c:ath_descdma_alloc_desc() > on -HEAD) does the following: > > * creates a tag > * allocates a dmamap (bus_dmamap_create) - storing it in dd->dd_dmamap; > * allocates memory via bus_dmamem_alloc - also storing it in dd->dd_dmamap. > > Now, I saw some NULL pointer derefernce going on when thigns failed to > load - and what I found was bus_dmamem_alloc() overwrites the dmat > pointer passed in (dd_dmamap above). So the dmamap allocated via > bus_dmamap_create() is just plain overwritten. > > I'm guessing that when allocating memory via bus_dmamem_alloc(), the > call to bus_dmamap_create() (and the bus_dmamap_destroy()) isn't > needed. > > Scott/mips people - what do you think? That bug isn't so easy to figure out with my 5 second attention span... Warner > > > Adrian > _______________________________________________ > freebsd-mips@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-mips > To unsubscribe, send any mail to "freebsd-mips-unsubscribe@freebsd.org"
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