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gfs2: Fix sign extension bug in gfs2_update_stats

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Commit 4d207133e9 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: 4d207133e9 ("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+
This commit is contained in:
Andreas Gruenbacher 2019-05-17 19:18:43 +01:00
parent a188339ca5
commit 5a5ec83d6a
1 changed files with 5 additions and 4 deletions
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9
fs/gfs2/lock_dlm.c
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@ -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;
}
/**