On Tue, 8 May 2007, Oliver Neukum wrote:
> Hi,
>
> this shows how the anchors can be used for doing reset support.
> Hibernate, when we get it should be similar.
I'll have more comments on this later.
But first, I think we should be able to get rid of the skel_open_lock
mutex plus similar mutexes in other USB drivers. The problem they address
is the race between open() and disconnect() -- or more accurately, open()
and unregister_dev(). It should be fixed once and for all in usbcore.
And without relying on the BKL.
How do you like this approach?
Alan Stern
Index: usb-2.6/drivers/usb/core/file.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/file.c
+++ usb-2.6/drivers/usb/core/file.c
@@ -16,15 +16,15 @@
*/
#include <linux/module.h>
-#include <linux/spinlock.h>
#include <linux/errno.h>
+#include <linux/rwsem.h>
#include <linux/usb.h>
#include "usb.h"
#define MAX_USB_MINORS 256
static const struct file_operations *usb_minors[MAX_USB_MINORS];
-static DEFINE_SPINLOCK(minor_lock);
+static DECLARE_RWSEM(minor_rwsem);
static int usb_open(struct inode * inode, struct file * file)
{
@@ -33,14 +33,11 @@ static int usb_open(struct inode * inode
int err = -ENODEV;
const struct file_operations *old_fops, *new_fops = NULL;
- spin_lock (&minor_lock);
+ down_read(&minor_rwsem);
c = usb_minors[minor];
- if (!c || !(new_fops = fops_get(c))) {
- spin_unlock(&minor_lock);
- return err;
- }
- spin_unlock(&minor_lock);
+ if (!c || !(new_fops = fops_get(c)))
+ goto done;
old_fops = file->f_op;
file->f_op = new_fops;
@@ -52,6 +49,8 @@ static int usb_open(struct inode * inode
file->f_op = fops_get(old_fops);
}
fops_put(old_fops);
+ done:
+ up_read(&minor_rwsem);
return err;
}
@@ -124,7 +123,7 @@ int usb_register_dev(struct usb_interfac
if (class_driver->fops == NULL)
goto exit;
- spin_lock (&minor_lock);
+ down_write(&minor_rwsem);
for (minor = minor_base; minor < MAX_USB_MINORS; ++minor) {
if (usb_minors[minor])
continue;
@@ -134,7 +133,7 @@ int usb_register_dev(struct usb_interfac
retval = 0;
break;
}
- spin_unlock (&minor_lock);
+ up_write(&minor_rwsem);
if (retval)
goto exit;
@@ -150,9 +149,9 @@ int usb_register_dev(struct usb_interfac
intf->usb_dev = device_create(&usb_class, &intf->dev,
MKDEV(USB_MAJOR, minor), "%s", temp);
if (IS_ERR(intf->usb_dev)) {
- spin_lock (&minor_lock);
+ down_write(&minor_rwsem);
usb_minors[intf->minor] = NULL;
- spin_unlock (&minor_lock);
+ up_write(&minor_rwsem);
retval = PTR_ERR(intf->usb_dev);
}
exit:
@@ -189,9 +188,9 @@ void usb_deregister_dev(struct usb_inter
dbg ("removing %d minor", intf->minor);
- spin_lock (&minor_lock);
+ down_write(&minor_rwsem);
usb_minors[intf->minor] = NULL;
- spin_unlock (&minor_lock);
+ up_write(&minor_rwsem);
snprintf(name, BUS_ID_SIZE, class_driver->name, intf->minor -
minor_base);
device_destroy(&usb_class, MKDEV(USB_MAJOR, intf->minor));
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