Re: [PATCH] drm: Remove the deprecated drm_put_dev() function
From: Sui Jingfeng
Date: Tue Jun 27 2023 - 06:23:21 EST
Hi,
On 2023/6/27 17:33, Jani Nikula wrote:
On Tue, 27 Jun 2023, Sui Jingfeng <suijingfeng@xxxxxxxxxxx> wrote:
Hi,
On 2023/6/26 15:48, Jani Nikula wrote:
On Sun, 25 Jun 2023, Sui Jingfeng <suijingfeng@xxxxxxxxxxx> wrote:
As this function can be replaced with drm_dev_unregister() + drm_dev_put(),
it is already marked as deprecated, so remove it. No functional change.
Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
---
drivers/gpu/drm/drm_drv.c | 28 ----------------------------
drivers/gpu/drm/drm_pci.c | 3 ++-
drivers/gpu/drm/radeon/radeon_drv.c | 3 ++-
include/drm/drm_drv.h | 1 -
4 files changed, 4 insertions(+), 31 deletions(-)
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 12687dd9e1ac..5057307fe22a 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -406,34 +406,6 @@ void drm_minor_release(struct drm_minor *minor)
* possibly leaving the hardware enabled.
*/
-/**
- * drm_put_dev - Unregister and release a DRM device
- * @dev: DRM device
- *
- * Called at module unload time or when a PCI device is unplugged.
- *
- * Cleans up all DRM device, calling drm_lastclose().
- *
- * Note: Use of this function is deprecated. It will eventually go away
- * completely. Please use drm_dev_unregister() and drm_dev_put() explicitly
- * instead to make sure that the device isn't userspace accessible any more
- * while teardown is in progress, ensuring that userspace can't access an
- * inconsistent state.
The last sentence is the crucial one. While the patch has no functional
changes,
But my patch help to save a useless check(if (!dev))
on where we found the check is not necessary.
```
- if (!dev) {
- DRM_ERROR("cleanup called no dev\n");
- return;
- }
```
I believe the goal never was to just mechanically replace one
call with the two.
The DRM core lose nothing, just a function wrapper.
Instead, this is probably a good chance to migrate the burden to the
driver side.
The point is to *fix* this stuff while doing the conversion. Anyone can
replace one function call with two, but that's just brushing the problem
under the carpet.
Interesting!
To be honest, I love you reviews.
I think, I probably be able to solve more practical problem,
This patch is just a trivial, I don't care much.
Can you help to have a look at my vgaarb patch set [1]
[1] https://patchwork.freedesktop.org/series/119250/
Really need you guidance there.
The current state is that we have a function the use of which is
potentially problematic, it's documented, and we can trivially locate
all the call sites.
I can merge the document to comments of the drm_dev_unregister() function,
remove the drm_put_dev function only. What do you think about this?
After your change, we've lost that information, and we haven't fixed
anything.
My understanding is that drm_dev_unregister() alone is enough to stop
the user-space
program accessing the kernel interface exposed.
```
radeon_pci_remove(struct pci_dev *pdev)
{
// should be called first in the pci remove funcition
drm_dev_unregister(dev);
// do the various(necessary) cleanup and free resource allocated
// call this function at the bottom of the radeon_pci_remove() function
drm_dev_put(dev);
}
```
And the drm_dev_unregister() function already told us, see below:
```
/**
* drm_dev_unregister - Unregister DRM device
* @dev: Device to unregister
*
* Unregister the DRM device from the system. This does the reverse of
* drm_dev_register() but does not deallocate the device. The caller
must call
* drm_dev_put() to drop their final reference, unless it is managed
with devres
* (as devices allocated with devm_drm_dev_alloc() are), in which case
there is
* already an unwind action registered.
*
* A special form of unregistering for hotpluggable devices is
drm_dev_unplug(),
* which can be called while there are still open users of @dev.
*
* This should be called first in the device teardown code to make sure
* userspace can't access the device instance any more.
*/
void drm_dev_unregister(struct drm_device *dev)
...
```
Thanks for the interesting remark again.
BR,
Jani.
I think the device driver(drm/radeon, for example) have better understanding
about how to ensure that userspace can't access an inconsistent state
than the DRM core.
BR,
Jani.
- */
-void drm_put_dev(struct drm_device *dev)
-{
- DRM_DEBUG("\n");
-
- if (!dev) {
- DRM_ERROR("cleanup called no dev\n");
- return;
- }
-
- drm_dev_unregister(dev);
- drm_dev_put(dev);
-}
-EXPORT_SYMBOL(drm_put_dev);
-
/**
* drm_dev_enter - Enter device critical section
* @dev: DRM device
diff --git a/drivers/gpu/drm/drm_pci.c b/drivers/gpu/drm/drm_pci.c
index 39d35fc3a43b..b3a68a92eaa6 100644
--- a/drivers/gpu/drm/drm_pci.c
+++ b/drivers/gpu/drm/drm_pci.c
@@ -257,7 +257,8 @@ void drm_legacy_pci_exit(const struct drm_driver *driver,
legacy_dev_list) {
if (dev->driver == driver) {
list_del(&dev->legacy_dev_list);
- drm_put_dev(dev);
+ drm_dev_unregister(dev);
+ drm_dev_put(dev);
}
}
mutex_unlock(&legacy_dev_list_lock);
diff --git a/drivers/gpu/drm/radeon/radeon_drv.c b/drivers/gpu/drm/radeon/radeon_drv.c
index e4374814f0ef..a4955ae10659 100644
--- a/drivers/gpu/drm/radeon/radeon_drv.c
+++ b/drivers/gpu/drm/radeon/radeon_drv.c
@@ -357,7 +357,8 @@ radeon_pci_remove(struct pci_dev *pdev)
{
struct drm_device *dev = pci_get_drvdata(pdev);
- drm_put_dev(dev);
+ drm_dev_unregister(dev);
+ drm_dev_put(dev);
}
static void
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 89e2706cac56..289c97b12e82 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -511,7 +511,6 @@ void drm_dev_unregister(struct drm_device *dev);
void drm_dev_get(struct drm_device *dev);
void drm_dev_put(struct drm_device *dev);
-void drm_put_dev(struct drm_device *dev);
bool drm_dev_enter(struct drm_device *dev, int *idx);
void drm_dev_exit(int idx);
void drm_dev_unplug(struct drm_device *dev);
--
Jingfeng