cfq_idle_class_timer: add paranoid checks for jiffies overflow
Oleg Nesterov [Wed, 7 Nov 2007 12:51:35 +0000 (13:51 +0100)]
In theory, if the queue was idle long enough, cfq_idle_class_timer may have
a false (and very long) timeout because jiffies can wrap into the past wrt
->last_end_request.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/cfq-iosched.c

index 6831a75..0b4a479 100644 (file)
@@ -789,6 +789,20 @@ static inline void cfq_slice_expired(struct cfq_data *cfqd, int timed_out)
                __cfq_slice_expired(cfqd, cfqq, timed_out);
 }
 
+static int start_idle_class_timer(struct cfq_data *cfqd)
+{
+       unsigned long end = cfqd->last_end_request + CFQ_IDLE_GRACE;
+       unsigned long now = jiffies;
+
+       if (time_before(now, end) &&
+           time_after_eq(now, cfqd->last_end_request)) {
+               mod_timer(&cfqd->idle_class_timer, end);
+               return 1;
+       }
+
+       return 0;
+}
+
 /*
  * Get next queue for service. Unless we have a queue preemption,
  * we'll simply select the first cfqq in the service tree.
@@ -805,19 +819,14 @@ static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
        cfqq = rb_entry(n, struct cfq_queue, rb_node);
 
        if (cfq_class_idle(cfqq)) {
-               unsigned long end;
-
                /*
                 * if we have idle queues and no rt or be queues had
                 * pending requests, either allow immediate service if
                 * the grace period has passed or arm the idle grace
                 * timer
                 */
-               end = cfqd->last_end_request + CFQ_IDLE_GRACE;
-               if (time_before(jiffies, end)) {
-                       mod_timer(&cfqd->idle_class_timer, end);
+               if (start_idle_class_timer(cfqd))
                        cfqq = NULL;
-               }
        }
 
        return cfqq;
@@ -2036,17 +2045,14 @@ out_cont:
 static void cfq_idle_class_timer(unsigned long data)
 {
        struct cfq_data *cfqd = (struct cfq_data *) data;
-       unsigned long flags, end;
+       unsigned long flags;
 
        spin_lock_irqsave(cfqd->queue->queue_lock, flags);
 
        /*
         * race with a non-idle queue, reset timer
         */
-       end = cfqd->last_end_request + CFQ_IDLE_GRACE;
-       if (!time_after_eq(jiffies, end))
-               mod_timer(&cfqd->idle_class_timer, end);
-       else
+       if (!start_idle_class_timer(cfqd))
                cfq_schedule_dispatch(cfqd);
 
        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);