From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C322C43215 for ; Fri, 22 Nov 2019 16:53:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DC7720672 for ; Fri, 22 Nov 2019 16:53:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727516AbfKVQxZ (ORCPT ); Fri, 22 Nov 2019 11:53:25 -0500 Received: from mga05.intel.com ([192.55.52.43]:27190 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726620AbfKVQxY (ORCPT ); Fri, 22 Nov 2019 11:53:24 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 22 Nov 2019 08:53:24 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,230,1571727600"; d="scan'208";a="205519460" Received: from djiang5-desk3.ch.intel.com ([143.182.136.137]) by fmsmga007.fm.intel.com with ESMTP; 22 Nov 2019 08:53:23 -0800 Subject: Re: [PATCH 1/5] dmaengine: Store module owner in dma_device struct To: Vinod Koul , Logan Gunthorpe Cc: linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, Dan Williams References: <20191022214616.7943-1-logang@deltatee.com> <20191022214616.7943-2-logang@deltatee.com> <20191109171853.GF952516@vkoul-mobl> <3a19f075-6a86-4ace-9184-227f3dc2f2d3@deltatee.com> <20191112055540.GY952516@vkoul-mobl> <5ca7ef5d-dda7-e36c-1d40-ef67612d2ac4@deltatee.com> <20191114045555.GJ952516@vkoul-mobl> <20191122052010.GO82508@vkoul-mobl> From: Dave Jiang Message-ID: <4c03b5c6-6f25-2753-22b9-7cdcb4f8b527@intel.com> Date: Fri, 22 Nov 2019 09:53:23 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191122052010.GO82508@vkoul-mobl> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/21/19 10:20 PM, Vinod Koul wrote: > On 14-11-19, 10:03, Logan Gunthorpe wrote: >> >> >> On 2019-11-13 9:55 p.m., Vinod Koul wrote: >>>> But that's the problem. We can't expect our users to be "nice" and not >>>> unbind when the driver is in use. Killing the kernel if the user >>>> unexpectedly unbinds is not acceptable. >>> >>> And that is why we review the code and ensure this does not happen and >>> behaviour is as expected >> >> Yes, but the current code can kill the kernel when the driver is unbound. >> >>>>>> I suspect this is less of an issue for most devices as they wouldn't >>>>>> normally be unbound while in use (for example there's really no reason >>>>>> to ever unbind IOAT seeing it's built into the system). Though, the fact >>>>>> is, the user could unbind these devices at anytime and we don't want to >>>>>> panic if they do. >>>>> >>>>> There are many drivers which do modules so yes I am expecting unbind and >>>>> even a bind following that to work >>>> >>>> Except they will panic if they unbind while in use, so that's a >>>> questionable definition of "work". >>> >>> dmaengine core has module reference so while they are being used they >>> won't be removed (unless I complete misread the driver core behaviour) >> >> Yes, as I mentioned in my other email, holding a module reference does >> not prevent the driver from being unbound. Any driver can be unbound by >> the user at any time without the module being removed. > > That sounds okay then. I'm actually glad Logan is putting some work in addressing this. I also ran into the same issue as well dealing with unbinds on my new driver. >> >> Essentially, at any time, a user can do this: >> >> echo 0000:83:00.4 > /sys/bus/pci/drivers/plx_dma/unbind >> >> Which will call plx_dma_remove() regardless of whether anyone has a >> reference to the module, and regardless of whether the dma channel is >> currently in use. I feel it is important that drivers support this >> without crashing, and my plx_dma driver does the correct thing here. >> >> Logan >