| From 5a5ec83d6ac974b12085cd99b196795f14079037 Mon Sep 17 00:00:00 2001 |
| From: Andreas Gruenbacher <agruenba@redhat.com> |
| Date: Fri, 17 May 2019 19:18:43 +0100 |
| Subject: gfs2: Fix sign extension bug in gfs2_update_stats |
| |
| 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; |
| } |
| |
| /** |
