md/raid5.c: add proper locking to error path of raid5_start_reshape.

If raid5_start_reshape errors out, we need to reset all the fields
that were updated (not just some), and need to use the seq_counter
to ensure make_request() doesn't use an inconsitent state.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index f013d3662665..4bbcb7e26d12 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -6384,12 +6384,18 @@ static int raid5_start_reshape(struct mddev *mddev)
         if (!mddev->sync_thread) {
                 mddev->recovery = 0;
                 spin_lock_irq(&conf->device_lock);
+                write_seqcount_begin(&conf->gen_lock);
                 mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
+                mddev->new_chunk_sectors =
+                        conf->chunk_sectors = conf->prev_chunk_sectors;
+                mddev->new_layout = conf->algorithm = conf->prev_algo;
                 rdev_for_each(rdev, mddev)
                         rdev->new_data_offset = rdev->data_offset;
                 smp_wmb();
+                conf->generation --;
                 conf->reshape_progress = MaxSector;
                 mddev->reshape_position = MaxSector;
+                write_seqcount_end(&conf->gen_lock);
                 spin_unlock_irq(&conf->device_lock);
                 return -EAGAIN;
         }