5 files changed, 21 insertions, 73 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 9d7621f271ff..08e0b11ba0a1 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -421,12 +421,6 @@ void btrfs_put_tree_mod_seq(struct btrfs_fs_info *fs_info,
         spin_unlock(&fs_info->tree_mod_seq_lock);
 
         /*
-         * we removed the lowest blocker from the blocker list, so there may be
-         * more processible delayed refs.
-         */
-        wake_up(&fs_info->tree_mod_seq_wait);
-
-        /*
          * anything that's lower than the lowest existing (read: blocked)
          * sequence number can be removed from the tree.
          */
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 348196350bf0..c38734a07a65 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1252,7 +1252,6 @@ struct btrfs_fs_info {
         atomic_t tree_mod_seq;
         struct list_head tree_mod_seq_list;
         struct seq_list tree_mod_seq_elem;
-        wait_queue_head_t tree_mod_seq_wait;
 
         /* this protects tree_mod_log */
         rwlock_t tree_mod_log_lock;
diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index da7419ed01bb..7561431af50d 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -662,9 +662,6 @@ int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info,
         add_delayed_tree_ref(fs_info, trans, &ref->node, bytenr,
                                    num_bytes, parent, ref_root, level, action,
                                    for_cow);
-        if (!need_ref_seq(for_cow, ref_root) &&
-            waitqueue_active(&fs_info->tree_mod_seq_wait))
-                wake_up(&fs_info->tree_mod_seq_wait);
         spin_unlock(&delayed_refs->lock);
         if (need_ref_seq(for_cow, ref_root))
                 btrfs_qgroup_record_ref(trans, &ref->node, extent_op);
@@ -713,9 +710,6 @@ int btrfs_add_delayed_data_ref(struct btrfs_fs_info *fs_info,
         add_delayed_data_ref(fs_info, trans, &ref->node, bytenr,
                                    num_bytes, parent, ref_root, owner, offset,
                                    action, for_cow);
-        if (!need_ref_seq(for_cow, ref_root) &&
-            waitqueue_active(&fs_info->tree_mod_seq_wait))
-                wake_up(&fs_info->tree_mod_seq_wait);
         spin_unlock(&delayed_refs->lock);
         if (need_ref_seq(for_cow, ref_root))
                 btrfs_qgroup_record_ref(trans, &ref->node, extent_op);
@@ -744,8 +738,6 @@ int btrfs_add_delayed_extent_op(struct btrfs_fs_info *fs_info,
                                    num_bytes, BTRFS_UPDATE_DELAYED_HEAD,
                                    extent_op->is_data);
 
-        if (waitqueue_active(&fs_info->tree_mod_seq_wait))
-                wake_up(&fs_info->tree_mod_seq_wait);
         spin_unlock(&delayed_refs->lock);
         return 0;
 }
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 502b20c56e84..a7ad8fc8dc53 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2035,8 +2035,6 @@ int open_ctree(struct super_block *sb,
         fs_info->free_chunk_space = 0;
         fs_info->tree_mod_log = RB_ROOT;
 
-        init_waitqueue_head(&fs_info->tree_mod_seq_wait);
-
         /* readahead state */
         INIT_RADIX_TREE(&fs_info->reada_tree, GFP_NOFS & ~__GFP_WAIT);
         spin_lock_init(&fs_info->reada_lock);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 45c69c4184c9..d3df65f83b5c 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2318,12 +2318,6 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
                 ref->in_tree = 0;
                 rb_erase(&ref->rb_node, &delayed_refs->root);
                 delayed_refs->num_entries--;
-                /*
-                 * we modified num_entries, but as we're currently running
-                 * delayed refs, skip
-                 *     wake_up(&delayed_refs->seq_wait);
-                 * here.
-                 */
                 spin_unlock(&delayed_refs->lock);
 
                 ret = run_one_delayed_ref(trans, root, ref, extent_op,
@@ -2350,22 +2344,6 @@ next:
         return count;
 }
 
-static void wait_for_more_refs(struct btrfs_fs_info *fs_info,
-                               struct btrfs_delayed_ref_root *delayed_refs,
-                               unsigned long num_refs,
-                               struct list_head *first_seq)
-{
-        spin_unlock(&delayed_refs->lock);
-        pr_debug("waiting for more refs (num %ld, first %p)\n",
-                 num_refs, first_seq);
-        wait_event(fs_info->tree_mod_seq_wait,
-                   num_refs != delayed_refs->num_entries ||
-                   fs_info->tree_mod_seq_list.next != first_seq);
-        pr_debug("done waiting for more refs (num %ld, first %p)\n",
-                 delayed_refs->num_entries, fs_info->tree_mod_seq_list.next);
-        spin_lock(&delayed_refs->lock);
-}
-
 #ifdef SCRAMBLE_DELAYED_REFS
 /*
  * Normally delayed refs get processed in ascending bytenr order. This
@@ -2460,13 +2438,11 @@ int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
         struct btrfs_delayed_ref_root *delayed_refs;
         struct btrfs_delayed_ref_node *ref;
         struct list_head cluster;
-        struct list_head *first_seq = NULL;
         int ret;
         u64 delayed_start;
         int run_all = count == (unsigned long)-1;
         int run_most = 0;
-        unsigned long num_refs = 0;
-        int consider_waiting;
+        int loops;
 
         /* We'll clean this up in btrfs_cleanup_transaction */
         if (trans->aborted)
@@ -2484,7 +2460,7 @@ int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
         delayed_refs = &trans->transaction->delayed_refs;
         INIT_LIST_HEAD(&cluster);
 again:
-        consider_waiting = 0;
+        loops = 0;
         spin_lock(&delayed_refs->lock);
 
 #ifdef SCRAMBLE_DELAYED_REFS
@@ -2512,31 +2488,6 @@ again:
                 if (ret)
                         break;
 
-                if (delayed_start >= delayed_refs->run_delayed_start) {
-                        if (consider_waiting == 0) {
-                                /*
-                                 * btrfs_find_ref_cluster looped. let's do one
-                                 * more cycle. if we don't run any delayed ref
-                                 * during that cycle (because we can't because
-                                 * all of them are blocked) and if the number of
-                                 * refs doesn't change, we avoid busy waiting.
-                                 */
-                                consider_waiting = 1;
-                                num_refs = delayed_refs->num_entries;
-                                first_seq = root->fs_info->tree_mod_seq_list.next;
-                        } else {
-                                wait_for_more_refs(root->fs_info, delayed_refs,
-                                                   num_refs, first_seq);
-                                /*
-                                 * after waiting, things have changed. we
-                                 * dropped the lock and someone else might have
-                                 * run some refs, built new clusters and so on.
-                                 * therefore, we restart staleness detection.
-                                 */
-                                consider_waiting = 0;
-                        }
-                }
-
                 ret = run_clustered_refs(trans, root, &cluster);
                 if (ret < 0) {
                         spin_unlock(&delayed_refs->lock);
@@ -2549,9 +2500,26 @@ again:
                 if (count == 0)
                         break;
 
-                if (ret || delayed_refs->run_delayed_start == 0) {
+                if (delayed_start >= delayed_refs->run_delayed_start) {
+                        if (loops == 0) {
+                                /*
+                                 * btrfs_find_ref_cluster looped. let's do one
+                                 * more cycle. if we don't run any delayed ref
+                                 * during that cycle (because we can't because
+                                 * all of them are blocked), bail out.
+                                 */
+                                loops = 1;
+                        } else {
+                                /*
+                                 * no runnable refs left, stop trying
+                                 */
+                                BUG_ON(run_all);
+                                break;
+                        }
+                }
+                if (ret) {
                         /* refs were run, let's reset staleness detection */
-                        consider_waiting = 0;
+                        loops = 0;
                 }
         }
 
@@ -5296,9 +5264,6 @@ static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
         rb_erase(&head->node.rb_node, &delayed_refs->root);
 
         delayed_refs->num_entries--;
-        smp_mb();
-        if (waitqueue_active(&root->fs_info->tree_mod_seq_wait))
-                wake_up(&root->fs_info->tree_mod_seq_wait);
 
         /*
          * we don't take a ref on the node because we're removing it from the