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Message-ID: <661d227b-5b99-7e38-c9fc-aed830755890@loongson.cn>
Date: Tue, 27 Jun 2023 17:55:39 +0800
From: Sui Jingfeng <suijingfeng@...ngson.cn>
To: Jani Nikula <jani.nikula@...ux.intel.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>,
Daniel Vetter <daniel@...ll.ch>,
Alex Deucher <alexander.deucher@....com>,
Christian Koenig <christian.koenig@....com>,
Pan Xinhui <Xinhui.Pan@....com>
Cc: amd-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm: Remove the deprecated drm_put_dev() function
Hi
On 2023/6/27 17:33, Jani Nikula wrote:
> On Tue, 27 Jun 2023, Sui Jingfeng <suijingfeng@...ngson.cn> wrote:
>> Hi,
>>
>> On 2023/6/26 15:48, Jani Nikula wrote:
>>> On Sun, 25 Jun 2023, Sui Jingfeng <suijingfeng@...ngson.cn> 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@...ngson.cn>
>>>> ---
>>>> 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.
Well, drm/i915 don't call this function either.
Only the drm/radeon call this function.
> 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.
But I do agree with you that the comments of this function are sort of
good quality document.
> After your change, we've lost that information, and we haven't fixed
> anything.
But back to the technique question, is it true that
the drm_dev_unregister() function alone can't guarantee
the device isn't userspace accessible any more ?
>
> 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
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