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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 943C1C432C3 for ; Thu, 14 Nov 2019 04:56:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 79C19206F4 for ; Thu, 14 Nov 2019 04:56:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573707362; bh=LE6qCswHlWOHnxEJs8IN+lZrqjVOccPKEwov1WrEzbA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=F2Xl9HkXB0ZFDZ8s9/+eF4v2ssebBVsIy9TjZ8kV25VLf490stQrEzzXVB0ZdDfc6 731P/b43IoBUtvCpP2E0eqDCIqtZSwEDW+BeDDVyAKtRsyFPf+MGXGdUGgNwARtf1N YQhoap5/vsofg2xnNolxtb35cDkVwj1T4OHiOcTE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726557AbfKNE4C (ORCPT ); Wed, 13 Nov 2019 23:56:02 -0500 Received: from mail.kernel.org ([198.145.29.99]:39044 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726505AbfKNE4C (ORCPT ); Wed, 13 Nov 2019 23:56:02 -0500 Received: from localhost (unknown [223.226.110.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8851C206EF; Thu, 14 Nov 2019 04:56:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573707361; bh=LE6qCswHlWOHnxEJs8IN+lZrqjVOccPKEwov1WrEzbA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bWfimNONXDwf2ajvcX+OY6WZbWg6+7vV1V+GrVwZ5R+0r0DvWhuZDbyWnKXFBqOeH c/8chMm4fpmkZk1F8I3J+5I7wbLM0QI/RJqLHXhzjcWB8Sr/X4G1RBUGo6xBPkKXgG 4iSO+pWDaYV1gxK2FP3y6yoLTMZnffn/1XVyYtRM= Date: Thu, 14 Nov 2019 10:25:55 +0530 From: Vinod Koul To: Logan Gunthorpe Cc: linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, Dan Williams Subject: Re: [PATCH 1/5] dmaengine: Store module owner in dma_device struct Message-ID: <20191114045555.GJ952516@vkoul-mobl> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5ca7ef5d-dda7-e36c-1d40-ef67612d2ac4@deltatee.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org On 12-11-19, 09:45, Logan Gunthorpe wrote: > > > On 2019-11-11 10:56 p.m., Vinod Koul wrote: > > On 11-11-19, 09:50, Logan Gunthorpe wrote: > >> > >> > >> On 2019-11-09 10:18 a.m., Vinod Koul wrote: > >>> Hi Logan, > >>> > >>> Sorry for delay in reply! > >>> > >>> On 22-10-19, 15:46, Logan Gunthorpe wrote: > >>>> dma_chan_to_owner() dereferences the driver from the struct device to > >>>> obtain the owner and call module_[get|put](). However, if the backing > >>>> device is unbound before the dma_device is unregistered, the driver > >>>> will be cleared and this will cause a NULL pointer dereference. > >>> > >>> Have you been able to repro this? If so how..? > >>> > >>> The expectation is that the driver shall unregister before removed. > >> > >> Yes, with my new driver, if I do a PCI unbind (which unregisters) while > >> the DMA engine is in use, it panics. The point is the underlying driver > >> can go away before the channel is removed. > > > > and in your driver remove you do not unregister? When unbind is invoked > > the driver remove is invoked by core and you should unregister whatever > > you have registered in your probe! > > > > Said that, if someone is using the dmaengine at that point of time, it > > is not a nice thing to do and can cause issues, but on idle it should > > just work! > > 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 > >> 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) -- ~Vinod