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>

6 files changed, 51 insertions, 9 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 4ddc8a8f82cd..acbce542d291 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -513,6 +513,7 @@ struct btrfs_fs_info {
         u64 alloc_start;
         struct btrfs_transaction *running_transaction;
         wait_queue_head_t transaction_throttle;
+        wait_queue_head_t transaction_wait;
         struct btrfs_super_block super_copy;
         struct btrfs_super_block super_for_commit;
         struct block_device *__bdev;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 66466d125c05..99bb385c2982 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1291,6 +1291,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
         mutex_init(&fs_info->cleaner_mutex);
         mutex_init(&fs_info->volume_mutex);
         init_waitqueue_head(&fs_info->transaction_throttle);
+        init_waitqueue_head(&fs_info->transaction_wait);
 
 #if 0
         ret = add_hasher(fs_info, "crc32c");
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 3e4e5c227c0c..d6505892cd52 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -251,7 +251,7 @@ static int noinline dirty_and_release_pages(struct btrfs_trans_handle *trans,
         end_of_last_block = start_pos + num_bytes - 1;
 
         lock_extent(io_tree, start_pos, end_of_last_block, GFP_NOFS);
-        trans = btrfs_start_transaction(root, 1);
+        trans = btrfs_join_transaction(root, 1);
         if (!trans) {
                 err = -ENOMEM;
                 goto out_unlock;
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index baf46017d0d3..0a687326c0b0 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -116,7 +116,7 @@ static int cow_file_range(struct inode *inode, u64 start, u64 end)
         struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
         int ret = 0;
 
-        trans = btrfs_start_transaction(root, 1);
+        trans = btrfs_join_transaction(root, 1);
         BUG_ON(!trans);
         btrfs_set_trans_block_group(trans, inode);
 
@@ -502,7 +502,7 @@ int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end,
                 return 0;
         }
 
-        trans = btrfs_start_transaction(root, 1);
+        trans = btrfs_join_transaction(root, 1);
 
         ordered_extent = btrfs_lookup_ordered_extent(inode, start);
         BUG_ON(!ordered_extent);
@@ -1812,7 +1812,7 @@ int btrfs_write_inode(struct inode *inode, int wait)
         int ret = 0;
 
         if (wait) {
-                trans = btrfs_start_transaction(root, 1);
+                trans = btrfs_join_transaction(root, 1);
                 btrfs_set_trans_block_group(trans, inode);
                 ret = btrfs_commit_transaction(trans, root);
         }
@@ -1830,7 +1830,7 @@ void btrfs_dirty_inode(struct inode *inode)
         struct btrfs_root *root = BTRFS_I(inode)->root;
         struct btrfs_trans_handle *trans;
 
-        trans = btrfs_start_transaction(root, 1);
+        trans = btrfs_join_transaction(root, 1);
         btrfs_set_trans_block_group(trans, inode);
         btrfs_update_inode(trans, root, inode);
         btrfs_end_transaction(trans, root);
@@ -2395,7 +2395,7 @@ again:
                                 free_extent_map(em);
                                 em = NULL;
                                 btrfs_release_path(root, path);
-                                trans = btrfs_start_transaction(root, 1);
+                                trans = btrfs_join_transaction(root, 1);
                                 goto again;
                         }
                         write_extent_buffer(leaf, map + pg_offset, ptr,
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);
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 910350cd4cf0..11fbdeceb26c 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -27,6 +27,7 @@ struct btrfs_transaction {
         int in_commit;
         int use_count;
         int commit_done;
+        int blocked;
         struct list_head list;
         struct extent_io_tree dirty_pages;
         unsigned long start_time;
@@ -75,6 +76,8 @@ int btrfs_end_transaction(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root);
 struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
                                                    int num_blocks);
+struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root,
+                                                   int num_blocks);
 int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root);
 int btrfs_commit_tree_roots(struct btrfs_trans_handle *trans,