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>

2 files changed, 13 insertions, 3 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);
 
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index bb1434dfec8a..8d8a6b7f8f5d 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -1290,7 +1290,8 @@ void drbd_bump_write_ordering(struct drbd_resource *resource, struct drbd_backin
         };
 
         pwo = resource->write_ordering;
-        wo = min(pwo, wo);
+        if (wo != WO_bdev_flush)
+                wo = min(pwo, wo);
         rcu_read_lock();
         idr_for_each_entry(&resource->devices, device, vnr) {
                 if (get_ldev(device)) {
@@ -1300,11 +1301,12 @@ void drbd_bump_write_ordering(struct drbd_resource *resource, struct drbd_backin
                         put_ldev(device);
                 }
         }
-        rcu_read_unlock();
 
         if (bdev)
                 wo = max_allowed_wo(bdev, wo);
 
+        rcu_read_unlock();
+
         resource->write_ordering = wo;
         if (pwo != resource->write_ordering || wo == WO_bdev_flush)
                 drbd_info(resource, "Method to ensure write ordering: %s\n", write_ordering_str[resource->write_ordering]);