md: raid5: avoid sector values going negative when testing reshape progress.
As sector_t in unsigned, we cannot afford to let 'safepos' etc go
negative.
So replace
a -= b;
by
a -= min(b,a);
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 4616bc3..3c3626d 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3811,13 +3811,13 @@
safepos = conf->reshape_safe;
sector_div(safepos, data_disks);
if (mddev->delta_disks < 0) {
- writepos -= reshape_sectors;
+ writepos -= min(reshape_sectors, writepos);
readpos += reshape_sectors;
safepos += reshape_sectors;
} else {
writepos += reshape_sectors;
- readpos -= reshape_sectors;
- safepos -= reshape_sectors;
+ readpos -= min(reshape_sectors, readpos);
+ safepos -= min(reshape_sectors, safepos);
}
/* 'writepos' is the most advanced device address we might write.