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Message-ID: <7941eb36-725e-72b5-67c7-1e3a9ae8f422@redhat.com>
Date: Thu, 1 Jun 2017 14:13:28 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: jeffy <jeffy.chen@...k-chips.com>,
Chris Wilson <chris@...is-wilson.co.uk>,
Sean Paul <seanpaul@...omium.org>,
linux-kernel@...r.kernel.org, briannorris@...omium.org,
dianders@...omium.org, tfiga@...omium.org, zyw@...k-chips.com,
marcheu@...omium.org, mark.yao@...k-chips.com, hshi@...omium.org,
Daniel Vetter <daniel.vetter@...el.com>,
Jani Nikula <jani.nikula@...ux.intel.com>,
dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
Tom Gundersen <teg@...m.no>,
Marco Diego Aurélio Mesquita
<marcodiegomesquita@...il.com>,
Patrik Jakobsson <patrik.r.jakobsson@...il.com>,
Dave Airlie <airlied@...hat.com>
Subject: Re: [PATCH v11] drm: Unplug drm device when unregistering it (v8)
Hi,
On 31-05-17 04:39, jeffy wrote:
> 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 <jeffy.chen@...k-chips.com>
>>>>>
>>>>> ---
>>>>
>>>> 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 <marcodiegomesquita@...il.com>
>>> Cc: Hans de Goede <hdegoede@...hat.com>
>>>
>>> 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.
Ah yes, I see. Still calling drm_dev_unregister() directly from
udl_usb_disconnect() is not going to work, see the patch titled
"drm: Fix oops + Xserver hang when unplugging USB drm devices"
The problem is that drm_dev_unregister() probably should be
split into a drm_dev_unregister() and drm_dev_cleanup()
function with the cleanup part getting called by the last unref,
and at least calling drm_lastclose and the driver->unload call
needs to be moved to the new drm_dev_cleanup.
However splitting drm_dev_unregister() into drm_dev_unregister()
and drm_dev_cleanup() is easier said then done because that
would change the teardown order (e.g. calling driver->unload
later) which may very well cause problems in various places
and drivers.
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);
>>>
>>
>>
>>
>
>
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