Re: [PATCH v11] drm: Unplug drm device when unregistering it (v8)
From: Hans de Goede
Date: Thu Jun 01 2017 - 08:13:39 EST
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@xxxxxxxxxxxxxx>
---
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 AurÃlio Mesquita <marcodiegomesquita@xxxxxxxxx>
Cc: Hans de Goede <hdegoede@xxxxxxxxxx>
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);