USB: fix race in autosuspend reschedule

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>

1 files changed, 16 insertions, 16 deletions

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 8c1eac27f2d..c27bc080d84 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -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.