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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

fs/btrfs/disk-io.c

+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,

fs/btrfs/extent-tree.c

+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);

fs/btrfs/transaction.h

+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;