Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 45ae2c18 authored by Nikolay Borisov's avatar Nikolay Borisov Committed by David Sterba
Browse files

btrfs: Document consistency of transaction->io_bgs list



The reason why io_bgs can be modified without holding any lock is
non-obvious. Document it and reference that documentation from the
respective call sites.

Signed-off-by: default avatarNikolay Borisov <nborisov@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent bf6d7d49
Loading
Loading
Loading
Loading
+4 −0
Original line number Diff line number Diff line
@@ -4346,6 +4346,10 @@ void btrfs_cleanup_dirty_bgs(struct btrfs_transaction *cur_trans,
	}
	spin_unlock(&cur_trans->dirty_bgs_lock);

	/*
	 * Refer to the definition of io_bgs member for details why it's safe
	 * to use it without any locking
	 */
	while (!list_empty(&cur_trans->io_bgs)) {
		cache = list_first_entry(&cur_trans->io_bgs,
					 struct btrfs_block_group_cache,
+7 −2
Original line number Diff line number Diff line
@@ -3741,8 +3741,9 @@ int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans)
				should_put = 0;

				/*
				 * the cache_write_mutex is protecting
				 * the io_list
				 * The cache_write_mutex is protecting the
				 * io_list, also refer to the definition of
				 * btrfs_transaction::io_bgs for more details
				 */
				list_add_tail(&cache->io_list, io);
			} else {
@@ -3934,6 +3935,10 @@ int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
	}
	spin_unlock(&cur_trans->dirty_bgs_lock);

	/*
	 * Refer to the definition of io_bgs member for details why it's safe
	 * to use it without any locking
	 */
	while (!list_empty(io)) {
		cache = list_first_entry(io, struct btrfs_block_group_cache,
					 io_list);
+16 −0
Original line number Diff line number Diff line
@@ -69,6 +69,22 @@ struct btrfs_transaction {
	struct list_head pending_chunks;
	struct list_head switch_commits;
	struct list_head dirty_bgs;

	/*
	 * There is no explicit lock which protects io_bgs, rather its
	 * consistency is implied by the fact that all the sites which modify
	 * it do so under some form of transaction critical section, namely:
	 *
	 * - btrfs_start_dirty_block_groups - This function can only ever be
	 *   run by one of the transaction committers. Refer to
	 *   BTRFS_TRANS_DIRTY_BG_RUN usage in btrfs_commit_transaction
	 *
	 * - btrfs_write_dirty_blockgroups - this is called by
	 *   commit_cowonly_roots from transaction critical section
	 *   (TRANS_STATE_COMMIT_DOING)
	 *
	 * - btrfs_cleanup_dirty_bgs - called on transaction abort
	 */
	struct list_head io_bgs;
	struct list_head dropped_roots;