drbd: allow write-ordering policy to be bumped up again

Previously, once you disabled flushes as a means of enforcing
write-ordering, you'd need to detach/re-attach to enable them again.

Allow drbdsetup disk-options to re-enable previously disabled
write-ordering policy options at runtime.

While at it fix RCU in drbd_bump_write_ordering()
max_allowed_wo() uses rcu_dereference, therefore it must
be called within rcu_read_lock()/rcu_read_unlock()

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 0bf8a6082bb8..66065e60fdbc 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1294,6 +1294,13 @@ static unsigned int drbd_al_extents_max(struct drbd_backing_dev *bdev)
         return (al_size_4k - 1) * AL_CONTEXT_PER_TRANSACTION;
 }
 
+static bool write_ordering_changed(struct disk_conf *a, struct disk_conf *b)
+{
+        return  a->disk_barrier != b->disk_barrier ||
+                a->disk_flushes != b->disk_flushes ||
+                a->disk_drain != b->disk_drain;
+}
+
 int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
 {
         struct drbd_config_context adm_ctx;
@@ -1400,7 +1407,8 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
         else
                 set_bit(MD_NO_FUA, &device->flags);
 
-        drbd_bump_write_ordering(device->resource, NULL, WO_bdev_flush);
+        if (write_ordering_changed(old_disk_conf, new_disk_conf))
+                drbd_bump_write_ordering(device->resource, NULL, WO_bdev_flush);
 
         drbd_md_sync(device);