USB: fix race in autosuspend reschedule
Alan Stern [Thu, 11 Oct 2007 20:47:36 +0000 (16:47 -0400)]
This patch (as1002) fixes a small race which can occur when a driver
expects usbcore to reschedule an autosuspend request.  If the request
arrives too late, it won't be rescheduled.  The patch adds an extra
argument to autosuspend_check(), indicating that a reschedule is
needed no matter how much time has elapsed.

It also tries to avoid letting asynchronous changes to the value of
jiffies cause a delay to become negative, by caching a local copy of
the current time.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/driver.c

index 8c1eac2..c27bc08 100644 (file)
@@ -950,11 +950,11 @@ done:
 #ifdef CONFIG_USB_SUSPEND
 
 /* Internal routine to check whether we may autosuspend a device. */
-static int autosuspend_check(struct usb_device *udev)
+static int autosuspend_check(struct usb_device *udev, int reschedule)
 {
        int                     i;
        struct usb_interface    *intf;
-       unsigned long           suspend_time;
+       unsigned long           suspend_time, j;
 
        /* For autosuspend, fail fast if anything is in use or autosuspend
         * is disabled.  Also fail if any interfaces require remote wakeup
@@ -996,20 +996,20 @@ static int autosuspend_check(struct usb_device *udev)
        }
 
        /* If everything is okay but the device hasn't been idle for long
-        * enough, queue a delayed autosuspend request.
+        * enough, queue a delayed autosuspend request.  If the device
+        * _has_ been idle for long enough and the reschedule flag is set,
+        * likewise queue a delayed (1 second) autosuspend request.
         */
-       if (time_after(suspend_time, jiffies)) {
+       j = jiffies;
+       if (time_before(j, suspend_time))
+               reschedule = 1;
+       else
+               suspend_time = j + HZ;
+       if (reschedule) {
                if (!timer_pending(&udev->autosuspend.timer)) {
-
-                       /* The value of jiffies may change between the
-                        * time_after() comparison above and the subtraction
-                        * below.  That's okay; the system behaves sanely
-                        * when a timer is registered for the present moment
-                        * or for the past.
-                        */
                        queue_delayed_work(ksuspend_usb_wq, &udev->autosuspend,
-                               round_jiffies_relative(suspend_time - jiffies));
-                       }
+                               round_jiffies_relative(suspend_time - j));
+               }
                return -EAGAIN;
        }
        return 0;
@@ -1017,7 +1017,7 @@ static int autosuspend_check(struct usb_device *udev)
 
 #else
 
-static inline int autosuspend_check(struct usb_device *udev)
+static inline int autosuspend_check(struct usb_device *udev, int reschedule)
 {
        return 0;
 }
@@ -1074,7 +1074,7 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
        udev->do_remote_wakeup = device_may_wakeup(&udev->dev);
 
        if (udev->auto_pm) {
-               status = autosuspend_check(udev);
+               status = autosuspend_check(udev, 0);
                if (status < 0)
                        goto done;
        }
@@ -1100,7 +1100,7 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
 
                /* Try another autosuspend when the interfaces aren't busy */
                if (udev->auto_pm)
-                       autosuspend_check(udev);
+                       autosuspend_check(udev, status == -EBUSY);
 
        /* If the suspend succeeded then prevent any more URB submissions,
         * flush any outstanding URBs, and propagate the suspend up the tree.