On 05/02/2024 16:16, Laurent Pinchart wrote:
> On Mon, Feb 05, 2024 at 04:11:43PM +0100, Hans Verkuil wrote:
>> On 20/12/2023 11:37, Sakari Ailus wrote:
>>> The list of file handles is needed to deliver media events as well as for
>>> other purposes in the future.
>>>
>>> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
>>> ---
>>> drivers/media/mc/mc-device.c | 23 ++++++++++++++++++++++-
>>> drivers/media/mc/mc-devnode.c | 2 +-
>>> include/media/media-devnode.h | 4 +++-
>>> 3 files changed, 26 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/media/mc/mc-device.c b/drivers/media/mc/mc-device.c
>>> index 67a39cb63f89..9cc055deeec9 100644
>>> --- a/drivers/media/mc/mc-device.c
>>> +++ b/drivers/media/mc/mc-device.c
>>> @@ -45,9 +45,11 @@ static inline void __user *media_get_uptr(__u64 arg)
>>> return (void __user *)(uintptr_t)arg;
>>> }
>>>
>>> -static int media_device_open(struct file *filp)
>>> +static int media_device_open(struct media_devnode *devnode, struct file *filp)
>>> {
>>> + struct media_device *mdev = to_media_device(devnode);
>>> struct media_device_fh *fh;
>>> + unsigned long flags;
>>>
>>> fh = kzalloc(sizeof(*fh), GFP_KERNEL);
>>> if (!fh)
>>> @@ -55,12 +57,23 @@ static int media_device_open(struct file *filp)
>>>
>>> filp->private_data = &fh->fh;
>>>
>>> + spin_lock_irqsave(&mdev->fh_list_lock, flags);
>>
>> The only reason for using the irqsave variant is because we want
>> to support events in the future, and those can be sent in irq context.
>
> Even in that case, would media_device_open() ever be called from
> interrupt context ? spin_lock_irqsave() is only needed if you don't know
> which context the function can be called from. If we know we'll be
> called from interruptible context only, you can use spin_lock_irq()
> instead.
Someone can call open() while at the same time the kernel sends a
media event from interrupt context. Such an event function will walk
over the fh_list. The irqsave here is meant to ensure that no event
interrupt can run while we add our fh to the fh list.
But without interrupts that access fh_list the irqsave variant is
confusing.
Regards,
Hans
>
>> But it is confusing to see this being used here when it is not yet
>> needed.
>>
>> At minimum this should be explained in the commit log.
>>
>>> + list_add(&fh->mdev_list, &mdev->fh_list);
>>> + spin_unlock_irqrestore(&mdev->fh_list_lock, flags);
>>> +
>>> return 0;
>>> }
>>>
>>> static int media_device_close(struct file *filp)
>>> {
>>> + struct media_devnode *devnode = media_devnode_data(filp);
>>> + struct media_device *mdev = to_media_device(devnode);
>>> struct media_device_fh *fh = media_device_fh(filp);
>>> + unsigned long flags;
>>> +
>>> + spin_lock_irqsave(&mdev->fh_list_lock, flags);
>>> + list_del(&fh->mdev_list);
>>> + spin_unlock_irqrestore(&mdev->fh_list_lock, flags);
>>>
>>> kfree(fh);
>>>
>>> @@ -769,11 +782,13 @@ void media_device_init(struct media_device *mdev)
>>> INIT_LIST_HEAD(&mdev->pads);
>>> INIT_LIST_HEAD(&mdev->links);
>>> INIT_LIST_HEAD(&mdev->entity_notify);
>>> + INIT_LIST_HEAD(&mdev->fh_list);
>>>
>>> mutex_init(&mdev->req_queue_mutex);
>>> mutex_init(&mdev->graph_mutex);
>>> ida_init(&mdev->entity_internal_idx);
>>> atomic_set(&mdev->request_id, 0);
>>> + spin_lock_init(&mdev->fh_list_lock);
>>>
>>> mdev->devnode.release = media_device_release;
>>> media_devnode_init(&mdev->devnode);
>>> @@ -824,6 +839,8 @@ EXPORT_SYMBOL_GPL(__media_device_register);
>>>
>>> void media_device_unregister(struct media_device *mdev)
>>> {
>>> + unsigned long flags;
>>> +
>>> if (mdev == NULL)
>>> return;
>>>
>>> @@ -834,6 +851,10 @@ void media_device_unregister(struct media_device *mdev)
>>> }
>>> mutex_unlock(&mdev->graph_mutex);
>>>
>>> + spin_lock_irqsave(&mdev->fh_list_lock, flags);
>>> + list_del_init(&mdev->fh_list);
>>> + spin_unlock_irqrestore(&mdev->fh_list_lock, flags);
>>> +
>>> device_remove_file(&mdev->devnode.dev, &dev_attr_model);
>>> dev_dbg(mdev->dev, "Media device unregistering\n");
>>> media_devnode_unregister(&mdev->devnode);
>>> diff --git a/drivers/media/mc/mc-devnode.c b/drivers/media/mc/mc-devnode.c
>>> index 04d376015526..0b5c24828e24 100644
>>> --- a/drivers/media/mc/mc-devnode.c
>>> +++ b/drivers/media/mc/mc-devnode.c
>>> @@ -171,7 +171,7 @@ static int media_open(struct inode *inode, struct file *filp)
>>> get_device(&devnode->dev);
>>> mutex_unlock(&media_devnode_lock);
>>>
>>> - ret = devnode->fops->open(filp);
>>> + ret = devnode->fops->open(devnode, filp);
>>> if (ret) {
>>> put_device(&devnode->dev);
>>> return ret;
>>> diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h
>>> index b0efdde4ffd8..840f7ae852d3 100644
>>> --- a/include/media/media-devnode.h
>>> +++ b/include/media/media-devnode.h
>>> @@ -21,6 +21,8 @@
>>> #include <linux/device.h>
>>> #include <linux/cdev.h>
>>>
>>> +struct media_devnode;
>>> +
>>> /*
>>> * Flag to mark the media_devnode struct as registered. Drivers must not touch
>>> * this flag directly, it will be set and cleared by media_devnode_register and
>>> @@ -49,7 +51,7 @@ struct media_file_operations {
>>> __poll_t (*poll) (struct file *, struct poll_table_struct *);
>>> long (*ioctl) (struct file *, unsigned int, unsigned long);
>>> long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
>>> - int (*open) (struct file *);
>>> + int (*open) (struct media_devnode *, struct file *);
>>> int (*release) (struct file *);
>>> };
>>>
>
