From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753624AbdKQAN6 (ORCPT ); Thu, 16 Nov 2017 19:13:58 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:34384 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753570AbdKQANv (ORCPT ); Thu, 16 Nov 2017 19:13:51 -0500 Date: Thu, 16 Nov 2017 16:13:50 -0800 From: Andrew Morton To: Cc: Christoph Hellwig , Robin Murphy , , , , , , Christoph Hellwig Subject: Re: [PATCH v4] dma-debug: fix incorrect pfn calculation Message-Id: <20171116161350.3b8bd1fbcaae8e032441d3e7@linux-foundation.org> In-Reply-To: <1510872972-23919-1-git-send-email-miles.chen@mediatek.com> References: <1510872972-23919-1-git-send-email-miles.chen@mediatek.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 17 Nov 2017 06:56:12 +0800 wrote: > From: Miles Chen > > dma-debug reports the following warning: > > [name:panic&]WARNING: CPU: 3 PID: 298 at kernel-4.4/lib/dma-debug.c:604 > debug _dma_assert_idle+0x1a8/0x230() > DMA-API: cpu touching an active dma mapped cacheline [cln=0x00000882300] > CPU: 3 PID: 298 Comm: vold Tainted: G W O 4.4.22+ #1 > Hardware name: MT6739 (DT) > Call trace: > [] dump_backtrace+0x0/0x1d4 > [] show_stack+0x14/0x1c > [] dump_stack+0xa8/0xe0 > [] warn_slowpath_common+0xf4/0x11c > [] warn_slowpath_fmt+0x60/0x80 > [] debug_dma_assert_idle+0x1a8/0x230 > [] wp_page_copy.isra.96+0x118/0x520 > [] do_wp_page+0x4fc/0x534 > [] handle_mm_fault+0xd4c/0x1310 > [] do_page_fault+0x1c8/0x394 > [] do_mem_abort+0x50/0xec > > I found that debug_dma_alloc_coherent() and debug_dma_free_coherent() > assume that dma_alloc_coherent() always returns a linear address. However > it's possible that dma_alloc_coherent() returns a non-linear address. In > this case, page_to_pfn(virt_to_page(virt)) will return an incorrect pfn. > If the pfn is valid and mapped as a COW page, we will hit the warning when > doing wp_page_copy(). > > Fix this by calculating pfn for linear and non-linear addresses. > It's a shame you didn't Cc Christoph, who was the sole reviewer of the earlier version. And it's a shame you didn't capture the result of that review discussion in the v3 changelog. And it's a shame that you didn't describe how this patch differs from earlier versions. Oh well, here's the incremental patch: --- a/lib/dma-debug.c~dma-debug-fix-incorrect-pfn-calculation-v4 +++ a/lib/dma-debug.c @@ -1495,15 +1495,22 @@ void debug_dma_alloc_coherent(struct dev if (!entry) return; + /* handle vmalloc and linear addresses */ + if (!is_vmalloc_addr(virt) && !virt_to_page(virt)) + return; + entry->type = dma_debug_coherent; entry->dev = dev; - entry->pfn = is_vmalloc_addr(virt) ? vmalloc_to_pfn(virt) : - page_to_pfn(virt_to_page(virt)); entry->offset = offset_in_page(virt); entry->size = size; entry->dev_addr = dma_addr; entry->direction = DMA_BIDIRECTIONAL; + if (is_vmalloc_addr(virt)) + entry->pfn = vmalloc_to_pfn(virt); + else + entry->pfn = page_to_pfn(virt_to_page(virt)); + add_dma_entry(entry); } EXPORT_SYMBOL(debug_dma_alloc_coherent); @@ -1514,14 +1521,21 @@ void debug_dma_free_coherent(struct devi struct dma_debug_entry ref = { .type = dma_debug_coherent, .dev = dev, - .pfn = is_vmalloc_addr(virt) ? vmalloc_to_pfn(virt) : - page_to_pfn(virt_to_page(virt)), .offset = offset_in_page(virt), .dev_addr = addr, .size = size, .direction = DMA_BIDIRECTIONAL, }; + /* handle vmalloc and linear addresses */ + if (!is_vmalloc_addr(virt) && !virt_to_page(virt)) + return; + + if (is_vmalloc_addr(virt)) + ref.pfn = vmalloc_to_pfn(virt); + else + ref.pfn = page_to_pfn(virt_to_page(virt)); + if (unlikely(dma_debug_disabled())) return; _