usbcore: cdev lock_kernel() pushdown

usb_open() is protected by a down_read(&minor_rwsem), but I'm not sure I
trust it to protect everything including subsidiary open() functions.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c
index 8133c99c6c5c..c6a95395e52a 100644
--- a/drivers/usb/core/file.c
+++ b/drivers/usb/core/file.c
@@ -18,6 +18,7 @@
 #include <linux/module.h>
 #include <linux/errno.h>
 #include <linux/rwsem.h>
+#include <linux/smp_lock.h>
 #include <linux/usb.h>
 
 #include "usb.h"
@@ -33,6 +34,7 @@ static int usb_open(struct inode * inode, struct file * file)
         int err = -ENODEV;
         const struct file_operations *old_fops, *new_fops = NULL;
 
+        lock_kernel();
         down_read(&minor_rwsem);
         c = usb_minors[minor];
 
@@ -51,6 +53,7 @@ static int usb_open(struct inode * inode, struct file * file)
         fops_put(old_fops);
  done:
         up_read(&minor_rwsem);
+        unlock_kernel();
         return err;
 }