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: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index dcfdb1f..08e33f3 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -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,