Btrfs: change how we wait for pending ordered extents

We have a mechanism to make sure we don't lose updates for ordered extents that
were logged in the transaction that is currently running.  We add the ordered
extent to a transaction list and then the transaction waits on all the ordered
extents in that list.  However are substantially large file systems this list
can be extremely large, and can give us soft lockups, since the ordered extents
don't remove themselves from the list when they do complete.

To fix this we simply add a counter to the transaction that is incremented any
time we have a logged extent that needs to be completed in the current
transaction.  Then when the ordered extent finally completes it decrements the
per transaction counter and wakes up the transaction if we are the last ones.
This will eliminate the softlockup.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 6 insertions, 28 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 9354e7a1247f..68a56c3cc555 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -232,6 +232,7 @@ loop:
 	extwriter_counter_init(cur_trans, type);
 	init_waitqueue_head(&cur_trans->writer_wait);
 	init_waitqueue_head(&cur_trans->commit_wait);
+	init_waitqueue_head(&cur_trans->pending_wait);
 	cur_trans->state = TRANS_STATE_RUNNING;
 	/*
 	 * One for this trans handle, one so it will live on until we
@@ -239,6 +240,7 @@ loop:
 	 */
 	atomic_set(&cur_trans->use_count, 2);
 	cur_trans->have_free_bgs = 0;
+	atomic_set(&cur_trans->pending_ordered, 0);
 	cur_trans->start_time = get_seconds();
 	cur_trans->dirty_bg_run = 0;
 
@@ -266,7 +268,6 @@ loop:
 	INIT_LIST_HEAD(&cur_trans->pending_snapshots);
 	INIT_LIST_HEAD(&cur_trans->pending_chunks);
 	INIT_LIST_HEAD(&cur_trans->switch_commits);
-	INIT_LIST_HEAD(&cur_trans->pending_ordered);
 	INIT_LIST_HEAD(&cur_trans->dirty_bgs);
 	INIT_LIST_HEAD(&cur_trans->io_bgs);
 	INIT_LIST_HEAD(&cur_trans->dropped_roots);
@@ -551,7 +552,6 @@ again:
 	h->can_flush_pending_bgs = true;
 	INIT_LIST_HEAD(&h->qgroup_ref_list);
 	INIT_LIST_HEAD(&h->new_bgs);
-	INIT_LIST_HEAD(&h->ordered);
 
 	smp_mb();
 	if (cur_trans->state >= TRANS_STATE_BLOCKED &&
@@ -784,12 +784,6 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 	if (!list_empty(&trans->new_bgs))
 		btrfs_create_pending_block_groups(trans, root);
 
-	if (!list_empty(&trans->ordered)) {
-		spin_lock(&info->trans_lock);
-		list_splice_init(&trans->ordered, &cur_trans->pending_ordered);
-		spin_unlock(&info->trans_lock);
-	}
-
 	trans->delayed_ref_updates = 0;
 	if (!trans->sync) {
 		must_run_delayed_refs =
@@ -1788,25 +1782,10 @@ static inline void btrfs_wait_delalloc_flush(struct btrfs_fs_info *fs_info)
 }
 
 static inline void
-btrfs_wait_pending_ordered(struct btrfs_transaction *cur_trans,
-			   struct btrfs_fs_info *fs_info)
+btrfs_wait_pending_ordered(struct btrfs_transaction *cur_trans)
 {
-	struct btrfs_ordered_extent *ordered;
-
-	spin_lock(&fs_info->trans_lock);
-	while (!list_empty(&cur_trans->pending_ordered)) {
-		ordered = list_first_entry(&cur_trans->pending_ordered,
-					   struct btrfs_ordered_extent,
-					   trans_list);
-		list_del_init(&ordered->trans_list);
-		spin_unlock(&fs_info->trans_lock);
-
-		wait_event(ordered->wait, test_bit(BTRFS_ORDERED_COMPLETE,
-						   &ordered->flags));
-		btrfs_put_ordered_extent(ordered);
-		spin_lock(&fs_info->trans_lock);
-	}
-	spin_unlock(&fs_info->trans_lock);
+	wait_event(cur_trans->pending_wait,
+		   atomic_read(&cur_trans->pending_ordered) == 0);
 }
 
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
@@ -1890,7 +1869,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	}
 
 	spin_lock(&root->fs_info->trans_lock);
-	list_splice_init(&trans->ordered, &cur_trans->pending_ordered);
 	if (cur_trans->state >= TRANS_STATE_COMMIT_START) {
 		spin_unlock(&root->fs_info->trans_lock);
 		atomic_inc(&cur_trans->use_count);
@@ -1949,7 +1927,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
 	btrfs_wait_delalloc_flush(root->fs_info);
 
-	btrfs_wait_pending_ordered(cur_trans, root->fs_info);
+	btrfs_wait_pending_ordered(cur_trans);
 
 	btrfs_scrub_pause(root);
 	/*