Date: Mon, 6 Aug 2012 12:41:50 -0700 From: Stanislav Sedov <stas@FreeBSD.org> To: John Baldwin <jhb@freebsd.org> Cc: arm@freebsd.org, Peter Jeremy <peter@rulingia.com>, mips@freebsd.org Subject: Re: On-stack allocation of DMA S/G lists Message-ID: <20120806124150.52fb0be17155cac723866d63@FreeBSD.org> In-Reply-To: <201208061026.06328.jhb@freebsd.org> References: <20120703111753.GB72292@server.rulingia.com> <20120708110516.GA38312@server.rulingia.com> <201207120826.05577.jhb@freebsd.org> <201208061026.06328.jhb@freebsd.org>
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On Mon, 6 Aug 2012 10:26:06 -0400 John Baldwin <jhb@freebsd.org> mentioned: > 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 > Seems to work fine for me on ARM. I had to initialize mflags to 0 in one place to get it compiling though. -- Stanislav Sedov ST4096-RIPE () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments
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