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USB: core: Remove usbfs_mutex 

Commit 4a2a8a2cce ("usbfs: private mutex for open, release, and
remove") is now obsolete.  The commit was created back when we had
to handle both usbfs device nodes and the old usbdevfs filesystem
(/proc/bus/usb/), but usbdevfs no longer exists.

This means there's no longer any need to hold a mutex during two
separate removal operations (and thus during an entire notifier chain
call).  Furthermore, the one remaining remove/release pair doesn't
race with open thanks to the synchronization provided by the device
model core in bus_find_device().  Remove and release don't race with
each other because they both run with the device lock held.

The upshot is that usbfs_mutex isn't needed any more.  This patch
removes it entirely.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
alistair/sunxi64-5.4-dsi
Alan Stern 2019-06-25 16:03:58 -04:00 committed by Greg Kroah-Hartman
parent 58ee01007c
commit ffed60971f
3 changed files with 0 additions and 13 deletions
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9
drivers/usb/core/devio.c
View File

@ -48,9 +48,6 @@
#define USB_DEVICE_MAX (USB_MAXBUS * 128)
#define USB_SG_SIZE 16384 /* split-size for large txs */
/* Mutual exclusion for removal, open, and release */
DEFINE_MUTEX(usbfs_mutex);
struct usb_dev_state {
struct list_head list; /* state list */
struct usb_device *dev;
@ -979,15 +976,9 @@ static int usbdev_open(struct inode *inode, struct file *file)
ret = -ENODEV;
/* Protect against simultaneous removal or release */
mutex_lock(&usbfs_mutex);
/* usbdev device-node */
if (imajor(inode) == USB_DEVICE_MAJOR)
dev = usbdev_lookup_by_devt(inode->i_rdev);
mutex_unlock(&usbfs_mutex);
if (!dev)
goto out_free_ps;

3
drivers/usb/core/notify.c
View File

@ -53,11 +53,8 @@ void usb_notify_add_device(struct usb_device *udev)
void usb_notify_remove_device(struct usb_device *udev)
{
/* Protect against simultaneous usbfs open */
mutex_lock(&usbfs_mutex);
blocking_notifier_call_chain(&usb_notifier_list,
USB_DEVICE_REMOVE, udev);
mutex_unlock(&usbfs_mutex);
}
void usb_notify_add_bus(struct usb_bus *ubus)

1
drivers/usb/core/usb.h
View File

@ -169,7 +169,6 @@ extern const struct attribute_group *usb_device_groups[];
extern const struct attribute_group *usb_interface_groups[];
/* usbfs stuff */
extern struct mutex usbfs_mutex;
extern struct usb_driver usbfs_driver;
extern const struct file_operations usbfs_devices_fops;
extern const struct file_operations usbdev_file_operations;