From c74c0d760e30f56f9699dc180036ca37993d1c58 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 15 Jul 2015 17:54:15 +1000 Subject: [PATCH] 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 --- drivers/md/raid5.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index e95219bf8859..19bbdbe1a52f 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -5388,11 +5388,16 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr, int *sk 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); } -- 2.39.2