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Subject[PATCH 4.19 016/276] gfs2: Fix sign extension bug in gfs2_update_stats
Date
From: Andreas Gruenbacher <agruenba@redhat.com>

commit 5a5ec83d6ac974b12085cd99b196795f14079037 upstream.

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+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/gfs2/lock_dlm.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- 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(str
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;
}

/**

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