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authorNikolay Borisov <nborisov@suse.com>2018-02-08 18:25:18 +0200
committerDavid Sterba <dsterba@suse.com>2018-03-26 15:09:34 +0200
commit45ae2c1841c31c90077cf427c09ea0e83e381026 (patch)
treeaad724668ba992f9e3128796be555a78081898c7 /fs/btrfs/transaction.h
parentbf6d7d4900c0d0c15dcd1baa1b65e6519bf4abef (diff)
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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>
Diffstat (limited to 'fs/btrfs/transaction.h')
-rw-r--r--fs/btrfs/transaction.h16
1 files changed, 16 insertions, 0 deletions
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 817fd7c9836b..2762c8d6191c 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -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;