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Message-ID: <47c5eca2-3624-edbc-bb2d-453645b6bf3b@redhat.com>
Date: Tue, 30 May 2017 09:06:57 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: Chris Wilson <chris@...is-wilson.co.uk>,
Sean Paul <seanpaul@...omium.org>,
Jeffy Chen <jeffy.chen@...k-chips.com>,
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 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.
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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