Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754064AbdDGHPp (ORCPT ); Fri, 7 Apr 2017 03:15:45 -0400 Received: from mail-wr0-f196.google.com ([209.85.128.196]:34593 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752887AbdDGHPk (ORCPT ); Fri, 7 Apr 2017 03:15:40 -0400 Date: Fri, 7 Apr 2017 09:15:31 +0200 From: Daniel Vetter To: jeffy Cc: Daniel Vetter , Sean Paul , Douglas Anderson , Brian Norris , Linux Kernel Mailing List , dri-devel , Tomasz Figa , "open list:ARM/Rockchip SoC..." , Chris Zhong , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v3 8/9] drm/rockchip: gem: Don't alloc/free gem buf when dev_private is invalid Message-ID: <20170407071531.2siqzefoddys6lut@phenom.ffwll.local> Mail-Followup-To: jeffy , Sean Paul , Douglas Anderson , Brian Norris , Linux Kernel Mailing List , dri-devel , Tomasz Figa , "open list:ARM/Rockchip SoC..." , Chris Zhong , "linux-arm-kernel@lists.infradead.org" References: <1491380967-28570-1-git-send-email-jeffy.chen@rock-chips.com> <1491380967-28570-9-git-send-email-jeffy.chen@rock-chips.com> <20170405162839.k6q4b3tpt6t2s3zm@art_vandelay> <20170406082612.qmwyfjr5uwcp3arr@phenom.ffwll.local> <58E621D7.3030205@rock-chips.com> <58E73535.4000409@rock-chips.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <58E73535.4000409@rock-chips.com> X-Operating-System: Linux phenom 4.9.0-2-amd64 User-Agent: NeoMutt/20170306 (1.8.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2085 Lines: 53 On Fri, Apr 07, 2017 at 02:44:05PM +0800, jeffy wrote: > Hi Daniel, > > On 04/07/2017 02:30 PM, Daniel Vetter wrote: > > On Thu, Apr 6, 2017 at 1:09 PM, jeffy wrote: > > > > > > On 04/06/2017 04:26 PM, Daniel Vetter wrote: > > > > > > > > On Wed, Apr 05, 2017 at 12:28:40PM -0400, Sean Paul wrote: > > > > > > > > > > On Wed, Apr 05, 2017 at 04:29:26PM +0800, Jeffy Chen wrote: > > > > > > > > > > > > After unbinding drm, the userspace may still has a chance to access > > > > > > gem buf. > > > > > > > > > > > > Add a sanity check for a NULL dev_private to prevent that from > > > > > > happening. > > > > > > > > > > > > > > > I still don't understand how this is happening. You're saying that these > > > > > hooks > > > > > can be called after rockchip_drm_unbind() has finished? > > > > > > > > > > > > Yeah this is supposed to be impossible. If it isn't, we need to debug and > > > > fix this properly. This smells like pretty bad duct-tape ... > > > > > > > > > it looks like after unbind, the user space may still own drm dev fd, and > > > could be able to call ioctl: > > > lrwx------. 1 chronos chronos 64 Mar 15 12:53 28 -> /dev/dri/card1 (deleted) > > > > > > and the drm_unplug_dev may help it, maybe we should call it in unbind? or > > > just break drm_ioctl when drm_dev not registered? > > > > Yes, by default unbind while userspace is running is totally broken in > > drm. drm_unplug_dev would be the fix, but it's only used by udl and > > not many use that. You might need to fix infrastructure up a bit. > please check this patch: > 9667071 New [v5,12/12] drm/drm_ioctl.c: Break ioctl when drm device > not registered > > > > For normal module unload the module reference will prevent unloading. > > So why exactly do you care about the unbind use-case? > sometimes we use unbind/bind for testing ;) Then make sure you stop your userspace first. Fixing unbind to be completely race-free requires a bit of work in the drm core. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch