Date: Mon, 2 Nov 2015 23:45:22 -0800 From: Jason Harmening <jason.harmening@gmail.com> To: Ian Lepore <ian@freebsd.org> Cc: Ganbold Tsagaankhuu <ganbold@gmail.com>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r289759 - in head/sys/arm: arm include Message-ID: <CAM=8qa=GX3yZmcXmMZz-nfmwOFhXyyKh_6%2BLVR=y7P5pURYvpQ@mail.gmail.com> In-Reply-To: <1446394311.91534.236.camel@freebsd.org> References: <201510221638.t9MGc1cc053885@repo.freebsd.org> <CAGtf9xOx_iSNqsPT7OdTmAy-ER_wFzOC9YxFigpQ%2B0wLj7=ytQ@mail.gmail.com> <56348FF8.3010602@gmail.com> <CAM=8qa=4EqPvRoUnMytQBe32GtvPRZRE_s34tOzmVNCLe8c=Fw@mail.gmail.com> <1446394311.91534.236.camel@freebsd.org>
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On Sun, Nov 1, 2015 at 8:11 AM, Ian Lepore <ian@freebsd.org> wrote: > > It's almost certainly not related to sysinit ordering. This exception > is happening during mmc probing after interrupts are enabled. > > It appears that the problem is the faulting code is running on one of > the very early pre-allocated kernel stacks (perhaps in an interrupt > handler on an idle thread stack), and these stacks are not in memory > represented in the vm page arrays. The mmc code is using a 64-byte > buffer on the stack and mapping it for DMA. Normally that causes a > bounce for cacheline alignment, but unluckily in this case that buffer > on the stack just happened to be aligned to a cacheline boundary and a > multiple of the cacheline size, so no bounce. That causes the new sync > logic that is based on keeping vm_page_t pointers and offsets to get a > NULL pointer back from PHYS_TO_VM_PAGE when mapping, then it dies at > sync time trying to dereference that. It used to work because the sync > logic used to use the vaddr, not a page pointer. > > Michal was working on a patch yesterday. > > Ah, thanks for pointing that out Ian. I was left scratching my head (admittedly on the road and w/o easy access to the code) wondering what on earth would be trying to do DMA during SI_SUB_CPU.
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