btrfs_start_transaction: wait for commits in progress to finish

btrfs_commit_transaction has to loop waiting for any writers in the
transaction to finish before it can proceed.  btrfs_start_transaction
should be polite and not join a transaction that is in the process
of being finished off.

There are a few places that can't wait, basically the ones doing IO that
might be needed to finish the transaction.  For them, btrfs_join_transaction
is added.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 40 insertions, 3 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 86a5acc19ce7..05823904ecba 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -62,6 +62,7 @@ static noinline int join_transaction(struct btrfs_root *root)
                 init_waitqueue_head(&cur_trans->writer_wait);
                 init_waitqueue_head(&cur_trans->commit_wait);
                 cur_trans->in_commit = 0;
+                cur_trans->blocked = 0;
                 cur_trans->use_count = 1;
                 cur_trans->commit_done = 0;
                 cur_trans->start_time = get_seconds();
@@ -99,14 +100,36 @@ static noinline int record_root_in_trans(struct btrfs_root *root)
         return 0;
 }
 
-struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
-                                                   int num_blocks)
+struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
+                                             int num_blocks, int join)
 {
         struct btrfs_trans_handle *h =
                 kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
+        struct btrfs_transaction *cur_trans;
         int ret;
 
         mutex_lock(&root->fs_info->trans_mutex);
+        cur_trans = root->fs_info->running_transaction;
+        if (cur_trans && cur_trans->blocked && !join) {
+                DEFINE_WAIT(wait);
+                cur_trans->use_count++;
+                while(1) {
+                        prepare_to_wait(&root->fs_info->transaction_wait, &wait,
+                                        TASK_UNINTERRUPTIBLE);
+                        if (cur_trans->blocked) {
+                                mutex_unlock(&root->fs_info->trans_mutex);
+                                schedule();
+                                mutex_lock(&root->fs_info->trans_mutex);
+                                finish_wait(&root->fs_info->transaction_wait,
+                                            &wait);
+                        } else {
+                                finish_wait(&root->fs_info->transaction_wait,
+                                            &wait);
+                                break;
+                        }
+                }
+                put_transaction(cur_trans);
+        }
         ret = join_transaction(root);
         BUG_ON(ret);
 
@@ -123,6 +146,17 @@ struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
         return h;
 }
 
+struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
+                                                   int num_blocks)
+{
+        return start_transaction(root, num_blocks, 0);
+}
+struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root,
+                                                   int num_blocks)
+{
+        return start_transaction(root, num_blocks, 1);
+}
+
 static noinline int wait_for_commit(struct btrfs_root *root,
                                     struct btrfs_transaction *commit)
 {
@@ -156,7 +190,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
         if (waitqueue_active(&cur_trans->writer_wait))
                 wake_up(&cur_trans->writer_wait);
 
-        if (cur_trans->in_commit && throttle) {
+        if (0 && cur_trans->in_commit && throttle) {
                 DEFINE_WAIT(wait);
                 mutex_unlock(&root->fs_info->trans_mutex);
                 prepare_to_wait(&root->fs_info->transaction_throttle, &wait,
@@ -617,6 +651,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
 printk("commit trans %Lu\n", trans->transid);
         trans->transaction->in_commit = 1;
+        trans->transaction->blocked = 1;
         cur_trans = trans->transaction;
         if (cur_trans->list.prev != &root->fs_info->trans_list) {
                 prev_trans = list_entry(cur_trans->list.prev,
@@ -684,7 +719,9 @@ printk("commit trans %Lu\n", trans->transid);
 
         btrfs_copy_pinned(root, pinned_copy);
 
+        trans->transaction->blocked = 0;
         wake_up(&root->fs_info->transaction_throttle);
+        wake_up(&root->fs_info->transaction_wait);
 
         mutex_unlock(&root->fs_info->trans_mutex);
         ret = btrfs_write_and_wait_transaction(trans, root);