On Fri, 3 Mar 2017, Ajay Kaher wrote:
> > usb_class->kref is not accessible outside the file.c
> > as usb_class is _static_ inside the file.c and
> > pointer of usb_class->kref is not passed anywhere.
> >
> > Hence as you wanted, there are no references of usb_class->kref
> > other than taken by init_usb_class() and released by destroy_usb_class().
>
> Verified the code again, I hope my last comments clarifed the things
> which came in your mind and helps you to accept the patch :)
Your main point is that usb_class->kref is accessed from only two
points, both of which are protected by the new mutex. This means there
is no reason for the value to be a struct kref at all. You should
change it to an int (and change its name). Leaving it as a kref will
make readers wonder why it needs to be updated atomically.
Also, why does destroy_usb_class() have that "if (usb_class) "test?
Isn't it true that usb_class can never be NULL there?
Alan Stern
> thanks,
> ajay kaher
>
>
> Signed-off-by: Ajay Kaher
>
> ---
>
> drivers/usb/core/file.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c
> index 822ced9..a12d184 100644
> --- a/drivers/usb/core/file.c
> +++ b/drivers/usb/core/file.c
> @@ -27,6 +27,7 @@
> #define MAX_USB_MINORS 256
> static const struct file_operations *usb_minors[MAX_USB_MINORS];
> static DECLARE_RWSEM(minor_rwsem);
> +static DEFINE_MUTEX(init_usb_class_mutex);
>
> static int usb_open(struct inode *inode, struct file *file)
> {
> @@ -109,8 +110,10 @@ static void release_usb_class(struct kref *kref)
>
> static void destroy_usb_class(void)
> {
> + mutex_lock(&init_usb_class_mutex);
> if (usb_class)
> kref_put(&usb_class->kref, release_usb_class);
> + mutex_unlock(&init_usb_class_mutex);
> }
>
> int usb_major_init(void)
> @@ -171,7 +174,10 @@ int usb_register_dev(struct usb_interface *intf,
> if (intf->minor >= 0)
> return -EADDRINUSE;
>
> + mutex_lock(&init_usb_class_mutex);
> retval = init_usb_class();
> + mutex_unlock(&init_usb_class_mutex);
> +
> if (retval)
> return retval;
>
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