btrfs: handle priority ticket failures in their respective helpers

Currently the error case for the priority tickets is handled where we
deal with all of the tickets, priority and non-priority.  This is OK in
general, but it makes for some awkward locking.  We take and drop the
space_info->lock back to back because of these different types of
tickets.

Rework the code to handle priority ticket failures in their respective
helpers.  This allows us to be less wonky with our space_info->lock
usage, and means that the main handler simply has to check
ticket->error, as the ticket is guaranteed to be off any list and
completely handled by the time it exits one of the handlers.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/space-info.c

@@ -1260,7 +1260,7 @@ static void priority_reclaim_metadata_space(struct btrfs_fs_info *fs_info,
 				int states_nr)
 {
 	u64 to_reclaim;
-	int flush_state;
+	int flush_state = 0;
 
 	spin_lock(&space_info->lock);
 	to_reclaim = btrfs_calc_reclaim_metadata_size(fs_info, space_info);
@@ -1268,10 +1268,9 @@ static void priority_reclaim_metadata_space(struct btrfs_fs_info *fs_info,
 		spin_unlock(&space_info->lock);
 		return;
 	}
-	spin_unlock(&space_info->lock);
 
-	flush_state = 0;
-	do {
+	while (flush_state < states_nr) {
+		spin_unlock(&space_info->lock);
 		flush_space(fs_info, space_info, to_reclaim, states[flush_state],
 			    false);
 		flush_state++;
@@ -1280,23 +1279,38 @@ static void priority_reclaim_metadata_space(struct btrfs_fs_info *fs_info,
 			spin_unlock(&space_info->lock);
 			return;
 		}
-		spin_unlock(&space_info->lock);
-	} while (flush_state < states_nr);
+	}
+
+	/*
+	 * We must run try_granting_tickets here because we could be a large
+	 * ticket in front of a smaller ticket that can now be satisfied with
+	 * the available space.
+	 */
+	ticket->error = -ENOSPC;
+	remove_ticket(space_info, ticket);
+	btrfs_try_granting_tickets(fs_info, space_info);
+	spin_unlock(&space_info->lock);
 }
 
 static void priority_reclaim_data_space(struct btrfs_fs_info *fs_info,
 					struct btrfs_space_info *space_info,
 					struct reserve_ticket *ticket)
 {
+	spin_lock(&space_info->lock);
 	while (!space_info->full) {
+		spin_unlock(&space_info->lock);
 		flush_space(fs_info, space_info, U64_MAX, ALLOC_CHUNK_FORCE, false);
 		spin_lock(&space_info->lock);
 		if (ticket->bytes == 0) {
 			spin_unlock(&space_info->lock);
 			return;
 		}
-		spin_unlock(&space_info->lock);
 	}
+
+	ticket->error = -ENOSPC;
+	remove_ticket(space_info, ticket);
+	btrfs_try_granting_tickets(fs_info, space_info);
+	spin_unlock(&space_info->lock);
 }
 
 static void wait_reserve_ticket(struct btrfs_fs_info *fs_info,
@@ -1378,25 +1392,7 @@ static int handle_reserve_ticket(struct btrfs_fs_info *fs_info,
 		break;
 	}
 
-	spin_lock(&space_info->lock);
 	ret = ticket->error;
-	if (ticket->bytes || ticket->error) {
-		/*
-		 * We were a priority ticket, so we need to delete ourselves
-		 * from the list.  Because we could have other priority tickets
-		 * behind us that require less space, run
-		 * btrfs_try_granting_tickets() to see if their reservations can
-		 * now be made.
-		 */
-		if (!list_empty(&ticket->list)) {
-			remove_ticket(space_info, ticket);
-			btrfs_try_granting_tickets(fs_info, space_info);
-		}
-
-		if (!ret)
-			ret = -ENOSPC;
-	}
-	spin_unlock(&space_info->lock);
 	ASSERT(list_empty(&ticket->list));
 	/*
 	 * Check that we can't have an error set if the reservation succeeded,