Btrfs: pass lockdep rwsem metadata to async commit transaction

The freeze rwsem is taken by sb_start_intwrite() and dropped during the
commit_ or end_transaction().  In the async case, that happens in a worker
thread.  Tell lockdep the calling thread is releasing ownership of the
rwsem and the async thread is picking it up.

XFS plays the same trick in fs/xfs/xfs_aops.c.

Signed-off-by: Sage Weil <sage@inktank.com>

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 27c2600..730c945 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1229,6 +1229,14 @@ static void do_async_commit(struct work_struct *work)
        struct btrfs_async_commit *ac =
                container_of(work, struct btrfs_async_commit, work.work);
 
+       /*
+        * We've got freeze protection passed with the transaction.
+        * Tell lockdep about it.
+        */
+       rwsem_acquire_read(
+               &ac->root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
+               0, 1, _THIS_IP_);
+
        btrfs_commit_transaction(ac->newtrans, ac->root);
        kfree(ac);
 }
@@ -1258,6 +1266,14 @@ int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans,
        atomic_inc(&cur_trans->use_count);
 
        btrfs_end_transaction(trans, root);
+
+       /*
+        * Tell lockdep we've released the freeze rwsem, since the
+        * async commit thread will be the one to unlock it.
+        */
+       rwsem_release(&root->fs_info->sb->s_writers.lock_map[SB_FREEZE_FS-1],
+                     1, _THIS_IP_);
+
        schedule_delayed_work(&ac->work, 0);
 
        /* wait for transaction to start and unblock */