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md/raid5: remove incorrect "min_t()" when calculating writepos.

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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>
This commit is contained in:
NeilBrown 2015-07-15 17:54:15 +10:00
parent 05256d9884
commit c74c0d760e
1 changed files with 6 additions and 1 deletions
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7
drivers/md/raid5.c
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@ -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);
}