From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758926Ab1LOPgW (ORCPT ); Thu, 15 Dec 2011 10:36:22 -0500 Received: from out3.smtp.messagingengine.com ([66.111.4.27]:39745 "EHLO out3.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751570Ab1LOPgV (ORCPT ); Thu, 15 Dec 2011 10:36:21 -0500 X-Sasl-enc: aFatUUFYEGGNz1WAC4SMKnykkfMfS+hHntYPS+hPxY/s 1323963380 Message-ID: <4EEA144A.4070108@ladisch.de> Date: Thu, 15 Dec 2011 16:37:46 +0100 From: Clemens Ladisch User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20111105 Thunderbird/8.0 MIME-Version: 1.0 To: Sebastian Andrzej Siewior CC: Alan Stern , Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] usb: fix number of mapped SG DMA entries References: <4EDAA59B.6080900@ladisch.de> <20111215123927.GA19650@linutronix.de> In-Reply-To: <20111215123927.GA19650@linutronix.de> 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 Sebastian Andrzej Siewior wrote: > * Alan Stern | 2011-12-04 11:59:32 [-0500]: >> On Sat, 3 Dec 2011, Clemens Ladisch wrote: >>> Add a new field num_mapped_sgs to struct urb so that we have a place to >>> store the number of mapped entries and can also retain the original >>> value of entries in num_sgs. Previously, usb_hcd_map_urb_for_dma() >>> would overwrite this with the number of mapped entries, which would >>> break dma_unmap_sg() because it requires the original number of entries. >>> >>> This fixes warnings like the following when using USB storage devices: >>> ------------[ cut here ]------------ >>> WARNING: at lib/dma-debug.c:902 check_unmap+0x4e4/0x695() >>> ehci_hcd 0000:00:12.2: DMA-API: device driver frees DMA sg list with different entry count [map count=4] [unmap count=1] >> >> Interesting. Do you have any idea why this warning didn't show up >> earlier? Is there perhaps a Kconfig option I ought to be using? > > My question here is why don't we map the complete sg list but only > one entry. What happens to the remaining few sg list entries? Don't we > sent too less data? Documentation/DMA-API.txt says: | Returns: the number of physical segments mapped (this may be shorter | than passed in if some elements of the scatter/gather list are | physically or virtually adjacent and an IOMMU maps them with a single | entry). > Is there anything special you do to get into this kind of situation? It appears that enabling CONFIG_DMA_API_DEBUG is quite special. :o) > Like 16GiB of memory on 32bit with highmem and a brutal disk/io test > case so? Plain x86-64; very few file operations done by hand. Regards, Clemens