btrfs: Factor out ref head locking code in __btrfs_run_delayed_refs

This is in preparation to refactor the giant loop in
__btrfs_run_delayed_refs. As a first step define a new function
which implements acquiring a reference to a btrfs_delayed_refs_head and
use it. 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 26fb9cbf380792d45aab9740c1957992bcf5357d..ee027a7fe7f481c24246051c3cdc8229c8f08e66 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2502,6 +2502,39 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans,
        return 0;
 }
 
+static struct btrfs_delayed_ref_head *btrfs_obtain_ref_head(
+                                       struct btrfs_trans_handle *trans)
+{
+       struct btrfs_delayed_ref_root *delayed_refs =
+               &trans->transaction->delayed_refs;
+       struct btrfs_delayed_ref_head *head = NULL;
+       int ret;
+
+       spin_lock(&delayed_refs->lock);
+       head = btrfs_select_ref_head(trans);
+       if (!head) {
+               spin_unlock(&delayed_refs->lock);
+               return head;
+       }
+
+       /*
+        * Grab the lock that says we are going to process all the refs for
+        * this head
+        */
+       ret = btrfs_delayed_ref_lock(trans, head);
+       spin_unlock(&delayed_refs->lock);
+
+       /*
+        * We may have dropped the spin lock to get the head mutex lock, and
+        * that might have given someone else time to free the head.  If that's
+        * true, it has been removed from our list and we can move on.
+        */
+       if (ret == -EAGAIN)
+               head = ERR_PTR(-EAGAIN);
+
+       return head;
+}
+
 /*
  * Returns 0 on success or if called with an already aborted transaction.
  * Returns -ENOMEM or -EIO on failure and will abort the transaction.
@@ -2526,24 +2559,10 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                        if (count >= nr)
                                break;
 
-                       spin_lock(&delayed_refs->lock);
-                       locked_ref = btrfs_select_ref_head(trans);
-                       if (!locked_ref) {
-                               spin_unlock(&delayed_refs->lock);
+                       locked_ref = btrfs_obtain_ref_head(trans);
+                       if (!locked_ref)
                                break;
-                       }
-
-                       /* grab the lock that says we are going to process
-                        * all the refs for this head */
-                       ret = btrfs_delayed_ref_lock(trans, locked_ref);
-                       spin_unlock(&delayed_refs->lock);
-                       /*
-                        * we may have dropped the spin lock to get the head
-                        * mutex lock, and that might have given someone else
-                        * time to free the head.  If that's true, it has been
-                        * removed from our list and we can move on.
-                        */
-                       if (ret == -EAGAIN) {
+                       else if (PTR_ERR(locked_ref) == -EAGAIN) {
                                locked_ref = NULL;
                                count++;
                                continue;