Date: Mon, 6 Aug 2012 10:26:06 -0400 From: John Baldwin <jhb@freebsd.org> To: Peter Jeremy <peter@rulingia.com> Cc: arm@freebsd.org, mips@freebsd.org Subject: On-stack allocation of DMA S/G lists Message-ID: <201208061026.06328.jhb@freebsd.org> In-Reply-To: <201207120826.05577.jhb@freebsd.org> References: <20120703111753.GB72292@server.rulingia.com> <20120708110516.GA38312@server.rulingia.com> <201207120826.05577.jhb@freebsd.org>
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On Thursday, July 12, 2012 8:26:05 am John Baldwin wrote: > On Sunday, July 08, 2012 7:05:16 am Peter Jeremy wrote: > > BTW(2): Whilst studying busdma_machdep.c for arm and mips, I've > > noticed they appear to potentially allocate substantial kernel stack > > under some conditions as several bus_dma(9) functions include: > > bus_dma_segment_t dm_segments[dmat->nsegments]; > > What prevents this overflowing the kernel stack? > > That does seem dubious. x86 stores the array in the tag instead. I have an untested patch to change bus-dma on arm and mips to allocate a dynamic S/G list in each DMA tag on first use instead of using on-stack allocation (which I think is rather bogus). Can folks review and test this patch please? Thanks. http://www.FreeBSD.org/~jhb/patches/arm_mips_dynamic_dma_segs.patch -- John Baldwin
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