From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751011AbdE3HHH (ORCPT ); Tue, 30 May 2017 03:07:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39040 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750867AbdE3HHD (ORCPT ); Tue, 30 May 2017 03:07:03 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 971D272497 Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=hdegoede@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 971D272497 Subject: Re: [PATCH v11] drm: Unplug drm device when unregistering it (v8) To: Chris Wilson , Sean Paul , Jeffy Chen , 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?Q?Marco_Diego_Aur=c3=a9lio_Mesquita?= , Patrik Jakobsson , Dave Airlie References: <1492068764-24353-1-git-send-email-jeffy.chen@rock-chips.com> <20170414151503.lmpp3udfuycavfki@art_vandelay> <20170529202512.GF23936@nuc-i3427.alporthouse.com> From: Hans de Goede Message-ID: <47c5eca2-3624-edbc-bb2d-453645b6bf3b@redhat.com> Date: Tue, 30 May 2017 09:06:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: <20170529202512.GF23936@nuc-i3427.alporthouse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 30 May 2017 07:07:03 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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); >