From owner-svn-src-head@freebsd.org Tue Nov 3 07:45:24 2015 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id B8CB5A24EFA; Tue, 3 Nov 2015 07:45:24 +0000 (UTC) (envelope-from jason.harmening@gmail.com) Received: from mail-lf0-x22b.google.com (mail-lf0-x22b.google.com [IPv6:2a00:1450:4010:c07::22b]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 3CACE14B8; Tue, 3 Nov 2015 07:45:24 +0000 (UTC) (envelope-from jason.harmening@gmail.com) Received: by lfbf136 with SMTP id f136so8130082lfb.0; Mon, 02 Nov 2015 23:45:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=5tH25XjvOUyj3CGuoiiMAODxEXxYDWHnLFx5g2RuzaQ=; b=sPCcS1OjMslqHIAKQMPYkkwrzPEFyYL66EFH9bU2EkUv8KVxCNwsBwowhwsAHtnoMG XRFhQqzaDNkHf8uVv+0S0U2y4waguIqKnBNomhlDxPotZz2sYN6c07kihhXLpYSnm81k L+56y/tUeh11NnL7W1OqdUHcobo52hX3G5PoAFr/g1CpGiiZ46Dxx200psK7MCG8Bchc tbqW8YX5n3zi1tNFyjVyF9Vn7t3WGM6dBLTm1NmYUSiSOtT7cle54PABNx4KzXGhGaYR gH353M9mCdIF08WfgLHh4o5JOQ3q85DsNmyEkvyJxRg5+SipLh27GQphyXy9wdrvNenC yNYg== MIME-Version: 1.0 X-Received: by 10.112.16.199 with SMTP id i7mr12293277lbd.105.1446536722391; Mon, 02 Nov 2015 23:45:22 -0800 (PST) Received: by 10.112.126.104 with HTTP; Mon, 2 Nov 2015 23:45:22 -0800 (PST) In-Reply-To: <1446394311.91534.236.camel@freebsd.org> References: <201510221638.t9MGc1cc053885@repo.freebsd.org> <56348FF8.3010602@gmail.com> <1446394311.91534.236.camel@freebsd.org> Date: Mon, 2 Nov 2015 23:45:22 -0800 Message-ID: Subject: Re: svn commit: r289759 - in head/sys/arm: arm include From: Jason Harmening To: Ian Lepore Cc: Ganbold Tsagaankhuu , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.20 X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Nov 2015 07:45:24 -0000 On Sun, Nov 1, 2015 at 8:11 AM, Ian Lepore 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.