Fix a gfs2 sign extension bug introduced in v4.3.

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Merge tag 'gfs2-5.1.fixes2' of git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2

Pull gfs2 fix from Andreas Gruenbacher:
 "Fix a gfs2 sign extension bug introduced in v4.3"

* tag 'gfs2-5.1.fixes2' of git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2:
  gfs2: Fix sign extension bug in gfs2_update_stats

fs/gfs2/lock_dlm.c

@@ -31,9 +31,10 @@
  * @delta is the difference between the current rtt sample and the
  * running average srtt. We add 1/8 of that to the srtt in order to
  * update the current srtt estimate. The variance estimate is a bit
- * more complicated. We subtract the abs value of the @delta from
+ * more complicated. We subtract the current variance estimate from
- * the current variance estimate and add 1/4 of that to the running
+ * the abs value of the @delta and add 1/4 of that to the running
- * total.
+ * total.  That's equivalent to 3/4 of the current variance
+ * estimate plus 1/4 of the abs of @delta.
  *
  * Note that the index points at the array entry containing the smoothed
  * mean value, and the variance is always in the following entry
@@ -49,7 +50,7 @@ static inline void gfs2_update_stats(struct gfs2_lkstats *s, unsigned index,
 	s64 delta = sample - s->stats[index];
 	s->stats[index] += (delta >> 3);
 	index++;
-	s->stats[index] += ((abs(delta) - s->stats[index]) >> 2);
+	s->stats[index] += (s64)(abs(delta) - s->stats[index]) >> 2;
 }
 
 /**