drbd: Removing drbd_cfg_rwsem

 * Updates to all configuration items is done under genl_lock().
   Including removal of mdevs or tconns.
 * All read non sleeping read sides are protected by rcu
 * All sleeping read sides keep reference counts to keep the
   objects alive

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

1 files changed, 15 insertions, 28 deletions

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index a0cf0005baf9..72ce3b0d0e03 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -335,10 +335,15 @@ static void conn_md_sync(struct drbd_tconn *tconn)
         struct drbd_conf *mdev;
         int vnr;
 
-        down_read(&drbd_cfg_rwsem);
-        idr_for_each_entry(&tconn->volumes, mdev, vnr)
+        rcu_read_lock();
+        idr_for_each_entry(&tconn->volumes, mdev, vnr) {
+                kref_get(&mdev->kref);
+                rcu_read_unlock();
                 drbd_md_sync(mdev);
-        up_read(&drbd_cfg_rwsem);
+                kref_put(&mdev->kref, &drbd_minor_destroy);
+                rcu_read_lock();
+        }
+        rcu_read_unlock();
 }
 
 int conn_khelper(struct drbd_tconn *tconn, char *cmd)
@@ -1193,12 +1198,12 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
                 rcu_assign_pointer(mdev->rs_plan_s, new_plan);
         }
 
+        mutex_unlock(&mdev->tconn->conf_update);
         drbd_md_sync(mdev);
 
         if (mdev->state.conn >= C_CONNECTED)
                 drbd_send_sync_param(mdev);
 
-        mutex_unlock(&mdev->tconn->conf_update);
         synchronize_rcu();
         kfree(old_disk_conf);
         kfree(old_plan);
@@ -2013,7 +2018,7 @@ int drbd_adm_connect(struct sk_buff *skb, struct genl_info *info)
         new_my_addr = (struct sockaddr *)&new_conf->my_addr;
         new_peer_addr = (struct sockaddr *)&new_conf->peer_addr;
 
-        /* No need to take drbd_cfg_rwsem here.  All reconfiguration is
+        /* No need for _rcu here. All reconfiguration is
          * strictly serialized on genl_lock(). We are protected against
          * concurrent reconfiguration/addition/deletion */
         list_for_each_entry(oconn, &drbd_tconns, all_tconn) {
@@ -2672,7 +2677,7 @@ int get_one_status(struct sk_buff *skb, struct netlink_callback *cb)
          */
 
         /* synchronize with conn_create()/conn_destroy() */
-        down_read(&drbd_cfg_rwsem);
+        rcu_read_lock();
         /* revalidate iterator position */
         list_for_each_entry_rcu(tmp, &drbd_tconns, all_tconn) {
                 if (pos == NULL) {
@@ -2738,7 +2743,7 @@ next_tconn:
         }
 
 out:
-        up_read(&drbd_cfg_rwsem);
+        rcu_read_unlock();
         /* where to start the next iteration */
         cb->args[0] = (long)pos;
         cb->args[1] = (pos == tconn) ? volume + 1 : 0;
@@ -3018,9 +3023,7 @@ int drbd_adm_add_minor(struct sk_buff *skb, struct genl_info *info)
                 goto out;
         }
 
-        down_write(&drbd_cfg_rwsem);
         retcode = conn_new_minor(adm_ctx.tconn, dh->minor, adm_ctx.volume);
-        up_write(&drbd_cfg_rwsem);
 out:
         drbd_adm_finish(info, retcode);
         return 0;
@@ -3053,9 +3056,7 @@ int drbd_adm_delete_minor(struct sk_buff *skb, struct genl_info *info)
         if (retcode != NO_ERROR)
                 goto out;
 
-        down_write(&drbd_cfg_rwsem);
         retcode = adm_delete_minor(adm_ctx.mdev);
-        up_write(&drbd_cfg_rwsem);
 out:
         drbd_adm_finish(info, retcode);
         return 0;
@@ -3078,52 +3079,43 @@ int drbd_adm_down(struct sk_buff *skb, struct genl_info *info)
                 goto out;
         }
 
-        down_read(&drbd_cfg_rwsem);
         /* demote */
         idr_for_each_entry(&adm_ctx.tconn->volumes, mdev, i) {
                 retcode = drbd_set_role(mdev, R_SECONDARY, 0);
                 if (retcode < SS_SUCCESS) {
                         drbd_msg_put_info("failed to demote");
-                        goto out_unlock;
+                        goto out;
                 }
         }
-        up_read(&drbd_cfg_rwsem);
 
-        /* disconnect; may stop the receiver;
-         * must not hold the drbd_cfg_rwsem */
         retcode = conn_try_disconnect(adm_ctx.tconn, 0);
         if (retcode < SS_SUCCESS) {
                 drbd_msg_put_info("failed to disconnect");
                 goto out;
         }
 
-        down_read(&drbd_cfg_rwsem);
         /* detach */
         idr_for_each_entry(&adm_ctx.tconn->volumes, mdev, i) {
                 retcode = adm_detach(mdev);
                 if (retcode < SS_SUCCESS) {
                         drbd_msg_put_info("failed to detach");
-                        goto out_unlock;
+                        goto out;
                 }
         }
-        up_read(&drbd_cfg_rwsem);
 
         /* If we reach this, all volumes (of this tconn) are Secondary,
          * Disconnected, Diskless, aka Unconfigured. Make sure all threads have
-         * actually stopped, state handling only does drbd_thread_stop_nowait().
-         * This needs to be done without holding drbd_cfg_rwsem. */
+         * actually stopped, state handling only does drbd_thread_stop_nowait(). */
         drbd_thread_stop(&adm_ctx.tconn->worker);
 
         /* Now, nothing can fail anymore */
 
         /* delete volumes */
-        down_write(&drbd_cfg_rwsem);
         idr_for_each_entry(&adm_ctx.tconn->volumes, mdev, i) {
                 retcode = adm_delete_minor(mdev);
                 if (retcode != NO_ERROR) {
                         /* "can not happen" */
                         drbd_msg_put_info("failed to delete volume");
-                        up_write(&drbd_cfg_rwsem);
                         goto out;
                 }
         }
@@ -3140,10 +3132,7 @@ int drbd_adm_down(struct sk_buff *skb, struct genl_info *info)
                 retcode = ERR_CONN_IN_USE;
                 drbd_msg_put_info("failed to delete connection");
         }
-        up_write(&drbd_cfg_rwsem);
         goto out;
-out_unlock:
-        up_read(&drbd_cfg_rwsem);
 out:
         drbd_adm_finish(info, retcode);
         return 0;
@@ -3159,7 +3148,6 @@ int drbd_adm_delete_connection(struct sk_buff *skb, struct genl_info *info)
         if (retcode != NO_ERROR)
                 goto out;
 
-        down_write(&drbd_cfg_rwsem);
         if (conn_lowest_minor(adm_ctx.tconn) < 0) {
                 list_del_rcu(&adm_ctx.tconn->all_tconn);
                 synchronize_rcu();
@@ -3169,7 +3157,6 @@ int drbd_adm_delete_connection(struct sk_buff *skb, struct genl_info *info)
         } else {
                 retcode = ERR_CONN_IN_USE;
         }
-        up_write(&drbd_cfg_rwsem);
 
         if (retcode == NO_ERROR)
                 drbd_thread_stop(&adm_ctx.tconn->worker);