cfq_idle_class_timer: add paranoid checks for jiffies overflow

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>

1 files changed, 17 insertions, 11 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 6831a758d541..0b4a47905575 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -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);