Hi everyone,

I think I tracked down the oops we were seeing Tsutomu Itoh's balance
test.  The delayed metadata insertion code was allowing delayed updates
to queue up and be process after the snapshot was created.

I've fixed this up by moving the delayed metadata run down into the
snapshot creation code, please take a look.  If nobody objects I'll have
this in the pull I send to Linus this weekend.


commit e999376f094162aa425ae749aa1df95ab928d010
Author: Chris Mason <chris.ma...@oracle.com>
Date:   Fri Jun 17 16:14:09 2011 -0400

    Btrfs: avoid delayed metadata items during commits
    
    Snapshot creation has two phases.  One is the initial snapshot setup,
    and the second is done during commit, while nobody is allowed to modify
    the root we are snapshotting.
    
    The delayed metadata insertion code can break that rule, it does a
    delayed inode update on the inode of the parent of the snapshot,
    and delayed directory item insertion.
    
    This makes sure to run the pending delayed operations before we
    record the snapshot root, which avoids corruptions.
    
    Signed-off-by: Chris Mason <chris.ma...@oracle.com>

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index fc515b7..f1cbd02 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1237,6 +1237,13 @@ again:
        return 0;
 }
 
+void btrfs_assert_delayed_root_empty(struct btrfs_root *root)
+{
+       struct btrfs_delayed_root *delayed_root;
+       delayed_root = btrfs_get_delayed_root(root);
+       WARN_ON(btrfs_first_delayed_node(delayed_root));
+}
+
 void btrfs_balance_delayed_items(struct btrfs_root *root)
 {
        struct btrfs_delayed_root *delayed_root;
diff --git a/fs/btrfs/delayed-inode.h b/fs/btrfs/delayed-inode.h
index cb79b67..d1a6a29 100644
--- a/fs/btrfs/delayed-inode.h
+++ b/fs/btrfs/delayed-inode.h
@@ -137,4 +137,8 @@ int btrfs_readdir_delayed_dir_index(struct file *filp, void 
*dirent,
 /* for init */
 int __init btrfs_delayed_inode_init(void);
 void btrfs_delayed_inode_exit(void);
+
+/* for debugging */
+void btrfs_assert_delayed_root_empty(struct btrfs_root *root);
+
 #endif
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c073d85..51dcec8 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -957,6 +957,15 @@ static noinline int create_pending_snapshot(struct 
btrfs_trans_handle *trans,
        ret = btrfs_update_inode(trans, parent_root, parent_inode);
        BUG_ON(ret);
 
+       /*
+        * pull in the delayed directory update
+        * and the delayed inode item
+        * otherwise we corrupt the FS during
+        * snapshot
+        */
+       ret = btrfs_run_delayed_items(trans, root);
+       BUG_ON(ret);
+
        record_root_in_trans(trans, root);
        btrfs_set_root_last_snapshot(&root->root_item, trans->transid);
        memcpy(new_root_item, &root->root_item, sizeof(*new_root_item));
@@ -1018,14 +1027,6 @@ static noinline int create_pending_snapshots(struct 
btrfs_trans_handle *trans,
        int ret;
 
        list_for_each_entry(pending, head, list) {
-               /*
-                * We must deal with the delayed items before creating
-                * snapshots, or we will create a snapthot with inconsistent
-                * information.
-               */
-               ret = btrfs_run_delayed_items(trans, fs_info->fs_root);
-               BUG_ON(ret);
-
                ret = create_pending_snapshot(trans, fs_info, pending);
                BUG_ON(ret);
        }
@@ -1319,15 +1320,21 @@ int btrfs_commit_transaction(struct btrfs_trans_handle 
*trans,
         */
        mutex_lock(&root->fs_info->reloc_mutex);
 
-       ret = create_pending_snapshots(trans, root->fs_info);
+       ret = btrfs_run_delayed_items(trans, root);
        BUG_ON(ret);
 
-       ret = btrfs_run_delayed_items(trans, root);
+       ret = create_pending_snapshots(trans, root->fs_info);
        BUG_ON(ret);
 
        ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
        BUG_ON(ret);
 
+       /*
+        * make sure none of the code above managed to slip in a
+        * delayed item
+        */
+       btrfs_assert_delayed_root_empty(root);
+
        WARN_ON(cur_trans != trans->transaction);
 
        btrfs_scrub_pause(root);
--
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