From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751076AbdEaCkU (ORCPT ); Tue, 30 May 2017 22:40:20 -0400 Received: from regular1.263xmail.com ([211.150.99.131]:34219 "EHLO regular1.263xmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750811AbdEaCkT (ORCPT ); Tue, 30 May 2017 22:40:19 -0400 X-263anti-spam: KSV:0; X-MAIL-GRAY: 0 X-MAIL-DELIVERY: 1 X-KSVirus-check: 0 X-ABS-CHECKED: 4 X-RL-SENDER: jeffy.chen@rock-chips.com X-FST-TO: hdegoede@redhat.com X-SENDER-IP: 103.29.142.67 X-LOGIN-NAME: jeffy.chen@rock-chips.com X-UNIQUE-TAG: <5dfb4eff35a1530252e062213e353e62> X-ATTACHMENT-NUM: 0 X-DNS-TYPE: 0 Message-ID: <592E2CD1.8080206@rock-chips.com> Date: Wed, 31 May 2017 10:39:13 +0800 From: jeffy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:19.0) Gecko/20130126 Thunderbird/19.0 MIME-Version: 1.0 To: Hans de Goede , Chris Wilson , Sean Paul , linux-kernel@vger.kernel.org, briannorris@chromium.org, dianders@chromium.org, tfiga@chromium.org, zyw@rock-chips.com, marcheu@chromium.org, mark.yao@rock-chips.com, hshi@chromium.org, Daniel Vetter , Jani Nikula , dri-devel@lists.freedesktop.org, David Airlie , Tom Gundersen , =?UTF-8?B?TWFyY28gRGllZ28gQXVyw6lsaW8gTWVzcXVpdGE=?= , Patrik Jakobsson , Dave Airlie Subject: Re: [PATCH v11] drm: Unplug drm device when unregistering it (v8) References: <1492068764-24353-1-git-send-email-jeffy.chen@rock-chips.com> <20170414151503.lmpp3udfuycavfki@art_vandelay> <20170529202512.GF23936@nuc-i3427.alporthouse.com> <47c5eca2-3624-edbc-bb2d-453645b6bf3b@redhat.com> In-Reply-To: <47c5eca2-3624-edbc-bb2d-453645b6bf3b@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Hans, thanx for investigating :) On 05/30/2017 03:06 PM, Hans de Goede wrote: > Hi, > > On 29-05-17 22:25, Chris Wilson wrote: >> On Fri, Apr 14, 2017 at 11:15:04AM -0400, Sean Paul wrote: >>> On Thu, Apr 13, 2017 at 03:32:44PM +0800, Jeffy Chen wrote: >>>> After unbinding drm, the user space may still owns the drm dev fd, and >>>> may still be able to call drm ioctl. >>>> >>>> We're using an unplugged state to prevent something like that, so let's >>>> reuse it here. >>>> >>>> Also drop drm_unplug_dev, because it would be unused after other >>>> changes. >>>> >>>> Verified on rk3399 chromebook kevin(with cros 4.4 kernel), no more >>>> crashes >>>> when unbinding drm with ui service still running. >>>> >>>> v2: Fix some commit messages. >>>> v3: Reuse unplug status. >>>> v4: Add drm_device_set_plug_state helper. >>>> v5: Fix hang when unregistering drm dev with open_count 0. >>>> v6: Move drm_device_set_plug_state into drm_drv. >>>> v7: Add missing drm_dev_unref in udl_drv. >>>> v8: Fix compiler errors after enable udl. >>>> >>>> Signed-off-by: Jeffy Chen >>>> >>>> --- >>> >>> Hi Jeffy, >>> Given the trouble we've had with this patch already, coupled with the >>> fact that >>> unbinding while userspace is active is a contrived/pathological case, >>> I don't >>> think it's worth picking this patch upstream. >>> >>> If it's really causing issues downstream, you can add my Reviewed-by >>> for a CHROMIUM >>> patch, but I'd rather not carry patches in the CrOS repo if we don't >>> need to. >> >> Would a >> >> Fixes: a39be606f99d ("drm: Do a full device unregister when unplugging") >> Reported-by: Marco Diego Aurélio Mesquita >> Cc: Hans de Goede >> >> convince us to look into this patch again? > > The problem is this patch is wrong, see below. > >>>> drivers/gpu/drm/drm_drv.c | 26 ++++++++++---------------- >>>> drivers/gpu/drm/udl/udl_drv.c | 3 ++- >>>> include/drm/drmP.h | 6 ------ >>>> include/drm/drm_drv.h | 1 - >>>> 4 files changed, 12 insertions(+), 24 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c >>>> index b5c6bb4..e1da4d1 100644 >>>> --- a/drivers/gpu/drm/drm_drv.c >>>> +++ b/drivers/gpu/drm/drm_drv.c >>>> @@ -355,22 +355,6 @@ void drm_put_dev(struct drm_device *dev) >>>> } >>>> EXPORT_SYMBOL(drm_put_dev); >>>> -void drm_unplug_dev(struct drm_device *dev) >>>> -{ >>>> - /* for a USB device */ >>>> - drm_dev_unregister(dev); >>>> - >>>> - mutex_lock(&drm_global_mutex); >>>> - >>>> - drm_device_set_unplugged(dev); >>>> - >>>> - if (dev->open_count == 0) { >>>> - drm_put_dev(dev); >>>> - } >>>> - mutex_unlock(&drm_global_mutex); >>>> -} >>>> -EXPORT_SYMBOL(drm_unplug_dev); >>>> - >>>> /* >>>> * DRM internal mount >>>> * We want to be able to allocate our own "struct address_space" >>>> to control >>>> @@ -733,6 +717,13 @@ static void remove_compat_control_link(struct >>>> drm_device *dev) >>>> kfree(name); >>>> } >>>> +static inline void drm_device_set_plug_state(struct drm_device *dev, >>>> + bool plugged) >>>> +{ >>>> + smp_wmb(); >>>> + atomic_set(&dev->unplugged, !plugged); >>>> +} >>>> + >>>> /** >>>> * drm_dev_register - Register DRM device >>>> * @dev: Device to register >>>> @@ -787,6 +778,8 @@ int drm_dev_register(struct drm_device *dev, >>>> unsigned long flags) >>>> if (drm_core_check_feature(dev, DRIVER_MODESET)) >>>> drm_modeset_register_all(dev); >>>> + drm_device_set_plug_state(dev, true); >>>> + >>>> ret = 0; >>>> DRM_INFO("Initialized %s %d.%d.%d %s for %s on minor %d\n", >>>> @@ -826,6 +819,7 @@ void drm_dev_unregister(struct drm_device *dev) >>>> drm_lastclose(dev); >>>> dev->registered = false; >>>> + drm_device_set_plug_state(dev, false); >>>> if (drm_core_check_feature(dev, DRIVER_MODESET)) >>>> drm_modeset_unregister_all(dev); >>>> diff --git a/drivers/gpu/drm/udl/udl_drv.c >>>> b/drivers/gpu/drm/udl/udl_drv.c >>>> index cd8b017..fc73e24 100644 >>>> --- a/drivers/gpu/drm/udl/udl_drv.c >>>> +++ b/drivers/gpu/drm/udl/udl_drv.c >>>> @@ -108,7 +108,8 @@ static void udl_usb_disconnect(struct >>>> usb_interface *interface) >>>> drm_kms_helper_poll_disable(dev); >>>> udl_fbdev_unplug(dev); >>>> udl_drop_usb(dev); >>>> - drm_unplug_dev(dev); >>>> + drm_dev_unregister(dev); >>>> + drm_dev_unref(dev); > > The unref here will cause the device struct to get free-ed even if > userspace still holds references to it through the drm_dev. To fix > this we would need to call drm_dev_ref on a open from userspace and > drm_dev_unref from drm_release. right, but i think we are already did the ref/unref in the open/release through drm_minor_acquire/drm_minor_release. i think the problem would be: 1/ we are trying to unregister&unref when disconnected 2/ the drm_release would try to unregister&unref(by calling drm_put_dev) when found it unplugged. and your patch "drm: Do not call drm_dev_unregister twice on drm_unplug_dev" looks like a good way to fix this(to me), maybe we can place this patch after yours, and check for open_count here? - drm_unplug_dev(dev); + if (dev->open_count == 0) + drm_dev_unref(dev); > > Regards, > > Hans > > > > >>>> } >>>> /* >>>> diff --git a/include/drm/drmP.h b/include/drm/drmP.h >>>> index 3bfafcd..980a204 100644 >>>> --- a/include/drm/drmP.h >>>> +++ b/include/drm/drmP.h >>>> @@ -488,12 +488,6 @@ static __inline__ int >>>> drm_core_check_feature(struct drm_device *dev, >>>> return ((dev->driver->driver_features & feature) ? 1 : 0); >>>> } >>>> -static inline void drm_device_set_unplugged(struct drm_device *dev) >>>> -{ >>>> - smp_wmb(); >>>> - atomic_set(&dev->unplugged, 1); >>>> -} >>>> - >>>> static inline int drm_device_is_unplugged(struct drm_device *dev) >>>> { >>>> int ret = atomic_read(&dev->unplugged); >>>> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h >>>> index 0fefc3f..eb63078 100644 >>>> --- a/include/drm/drm_drv.h >>>> +++ b/include/drm/drm_drv.h >>>> @@ -544,7 +544,6 @@ void drm_dev_unregister(struct drm_device *dev); >>>> void drm_dev_ref(struct drm_device *dev); >>>> void drm_dev_unref(struct drm_device *dev); >>>> void drm_put_dev(struct drm_device *dev); >>>> -void drm_unplug_dev(struct drm_device *dev); >>>> int drm_dev_set_unique(struct drm_device *dev, const char *name); >> > > >