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authorAndreas Gruenbacher2019-05-17 19:18:43 +0100
committerAndreas Gruenbacher2019-05-22 14:09:44 +0200
commit5a5ec83d6ac974b12085cd99b196795f14079037 (patch)
treeba7ac34e9dbe8e0795b3704e36d5bdb88dc01faa /fs
parenta188339ca5a396acc588e5851ed7e19f66b0ebd9 (diff)
gfs2: Fix sign extension bug in gfs2_update_stats
Commit 4d207133e9c3 changed the types of the statistic values in struct gfs2_lkstats from s64 to u64. Because of that, what should be a signed value in gfs2_update_stats turned into an unsigned value. When shifted right, we end up with a large positive value instead of a small negative value, which results in an incorrect variance estimate. Fixes: 4d207133e9c3 ("gfs2: Make statistics unsigned, suitable for use with do_div()") Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Cc: stable@vger.kernel.org # v4.4+
Diffstat (limited to 'fs')
-rw-r--r--fs/gfs2/lock_dlm.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/fs/gfs2/lock_dlm.c b/fs/gfs2/lock_dlm.c
index 31df26ed7854..69bd1597bacf 100644
--- a/fs/gfs2/lock_dlm.c
+++ b/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
- * the current variance estimate and add 1/4 of that to the running
- * total.
+ * more complicated. We subtract the current variance estimate from
+ * the abs value of the @delta and add 1/4 of that to the running
+ * 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;
}
/**