md/raid5: remove incorrect "min_t()" when calculating writepos.
This code is calculating:
writepos, which is the furthest along address (device-space) that we
*will* be writing to
readpos, which is the earliest address that we *could* possible read
from, and
safepos, which is the earliest address in the 'old' section that we
might read from after a crash when the reshape position is
recovered from metadata.
The first is a precise calculation, so clipping at zero doesn't
make sense. As the reshape position is now guaranteed to always be
a multiple of reshape_sectors and as we already BUG_ON when
reshape_progress is zero, there is no point in this min_t() call.
The readpos and safepos are worst case - actual value depends on
precise geometry. That worst case could be negative, which is only
a problem because we are storing the value in an unsigned.
So leave the min_t() for those.
Signed-off-by: NeilBrown <neilb@suse.com>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e95219b..19bbdbe 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5388,11 +5388,16 @@
safepos = conf->reshape_safe;
sector_div(safepos, data_disks);
if (mddev->reshape_backwards) {
- writepos -= min_t(sector_t, reshape_sectors, writepos);
+ BUG_ON(writepos < reshape_sectors);
+ writepos -= reshape_sectors;
readpos += reshape_sectors;
safepos += reshape_sectors;
} else {
writepos += reshape_sectors;
+ /* readpos and safepos are worst-case calculations.
+ * A negative number is overly pessimistic, and causes
+ * obvious problems for unsigned storage. So clip to 0.
+ */
readpos -= min_t(sector_t, reshape_sectors, readpos);
safepos -= min_t(sector_t, reshape_sectors, safepos);
}