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Commit 5a5ec83d authored by Andreas Gruenbacher's avatar Andreas Gruenbacher
Browse files

gfs2: Fix sign extension bug in gfs2_update_stats 



Commit 4d207133 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: 4d207133 ("gfs2: Make statistics unsigned, suitable for use with do_div()")
Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
Cc: stable@vger.kernel.org # v4.4+
parent a188339c

fs/gfs2/lock_dlm.c

+5 −4
Original line number Diff line number Diff line
@@ -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;

}



/**