Re: [PATCH v11] drm: Unplug drm device when unregistering it (v8)
From: jeffy
Date: Tue May 30 2017 - 22:40:26 EST
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.
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);