btrfs: refactor __btrfs_run_delayed_refs loop

Refactor the delayed refs loop by using the newly introduced
btrfs_run_delayed_refs_for_head function. This greatly simplifies
__btrfs_run_delayed_refs and makes it more obvious what is happening.

We now have 1 loop which iterates the existing delayed_heads and then
each selected ref head is processed by the new helper. All existing
semantics of the code are preserved so no functional changes.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 979702f..8798fa0 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2548,6 +2548,9 @@ static int btrfs_run_delayed_refs_for_head(struct btrfs_trans_handle *trans,
 
        delayed_refs = &trans->transaction->delayed_refs;
 
+       lockdep_assert_held(&locked_ref->mutex);
+       lockdep_assert_held(&locked_ref->lock);
+
        while ((ref = select_delayed_ref(locked_ref))) {
                if (ref->seq &&
                    btrfs_check_delayed_seq(fs_info, ref->seq)) {
@@ -2621,31 +2624,25 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
 {
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_delayed_ref_root *delayed_refs;
-       struct btrfs_delayed_ref_node *ref;
        struct btrfs_delayed_ref_head *locked_ref = NULL;
-       struct btrfs_delayed_extent_op *extent_op;
        ktime_t start = ktime_get();
        int ret;
        unsigned long count = 0;
        unsigned long actual_count = 0;
-       int must_insert_reserved = 0;
 
        delayed_refs = &trans->transaction->delayed_refs;
-       while (1) {
+       do {
                if (!locked_ref) {
-                       if (count >= nr)
-                               break;
-
                        locked_ref = btrfs_obtain_ref_head(trans);
-                       if (!locked_ref)
-                               break;
-                       else if (PTR_ERR(locked_ref) == -EAGAIN) {
-                               locked_ref = NULL;
-                               count++;
-                               continue;
+                       if (IS_ERR_OR_NULL(locked_ref)) {
+                               if (PTR_ERR(locked_ref) == -EAGAIN) {
+                                       continue;
+                               } else {
+                                       break;
+                               }
                        }
+                       count++;
                }
-
                /*
                 * We need to try and merge add/drops of the same ref since we
                 * can run into issues with relocate dropping the implicit ref
@@ -2661,23 +2658,19 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                spin_lock(&locked_ref->lock);
                btrfs_merge_delayed_refs(trans, delayed_refs, locked_ref);
 
-               ref = select_delayed_ref(locked_ref);
-
-               if (ref && ref->seq &&
-                   btrfs_check_delayed_seq(fs_info, ref->seq)) {
-                       spin_unlock(&locked_ref->lock);
-                       unselect_delayed_ref_head(delayed_refs, locked_ref);
-                       locked_ref = NULL;
-                       cond_resched();
-                       count++;
-                       continue;
-               }
-
-               /*
-                * We're done processing refs in this ref_head, clean everything
-                * up and move on to the next ref_head.
-                */
-               if (!ref) {
+               ret = btrfs_run_delayed_refs_for_head(trans, locked_ref,
+                                                     &actual_count);
+               if (ret < 0 && ret != -EAGAIN) {
+                       /*
+                        * Error, btrfs_run_delayed_refs_for_head already
+                        * unlocked everything so just bail out
+                        */
+                       return ret;
+               } else if (!ret) {
+                       /*
+                        * Success, perform the usual cleanup of a processed
+                        * head
+                        */
                        ret = cleanup_ref_head(trans, locked_ref);
                        if (ret > 0 ) {
                                /* We dropped our lock, we need to loop. */
@@ -2686,61 +2679,16 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                        } else if (ret) {
                                return ret;
                        }
-                       locked_ref = NULL;
-                       count++;
-                       continue;
                }
 
-               actual_count++;
-               ref->in_tree = 0;
-               rb_erase_cached(&ref->ref_node, &locked_ref->ref_tree);
-               RB_CLEAR_NODE(&ref->ref_node);
-               if (!list_empty(&ref->add_list))
-                       list_del(&ref->add_list);
                /*
-                * When we play the delayed ref, also correct the ref_mod on
-                * head
+                * Either success case or btrfs_run_delayed_refs_for_head
+                * returned -EAGAIN, meaning we need to select another head
                 */
-               switch (ref->action) {
-               case BTRFS_ADD_DELAYED_REF:
-               case BTRFS_ADD_DELAYED_EXTENT:
-                       locked_ref->ref_mod -= ref->ref_mod;
-                       break;
-               case BTRFS_DROP_DELAYED_REF:
-                       locked_ref->ref_mod += ref->ref_mod;
-                       break;
-               default:
-                       WARN_ON(1);
-               }
-               atomic_dec(&delayed_refs->num_entries);
-
-               /*
-                * Record the must-insert_reserved flag before we drop the spin
-                * lock.
-                */
-               must_insert_reserved = locked_ref->must_insert_reserved;
-               locked_ref->must_insert_reserved = 0;
 
-               extent_op = locked_ref->extent_op;
-               locked_ref->extent_op = NULL;
-               spin_unlock(&locked_ref->lock);
-
-               ret = run_one_delayed_ref(trans, ref, extent_op,
-                                         must_insert_reserved);
-
-               btrfs_free_delayed_extent_op(extent_op);
-               if (ret) {
-                       unselect_delayed_ref_head(delayed_refs, locked_ref);
-                       btrfs_put_delayed_ref(ref);
-                       btrfs_debug(fs_info, "run_one_delayed_ref returned %d",
-                                   ret);
-                       return ret;
-               }
-
-               btrfs_put_delayed_ref(ref);
-               count++;
+               locked_ref = NULL;
                cond_resched();
-       }
+       } while ((nr != -1 && count < nr) || locked_ref);
 
        /*
         * We don't want to include ref heads since we can have empty ref heads