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, 2 insertions, 2 deletions

diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index db6bfd92f0ea..bf7b1ddf5993 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -46,6 +46,7 @@ struct btrfs_transaction {
 	 */
 	atomic_t num_writers;
 	atomic_t use_count;
+	atomic_t pending_ordered;
 
 	/*
 	 * true if there is free bgs operations in this transaction
@@ -59,9 +60,9 @@ struct btrfs_transaction {
 	unsigned long start_time;
 	wait_queue_head_t writer_wait;
 	wait_queue_head_t commit_wait;
+	wait_queue_head_t pending_wait;
 	struct list_head pending_snapshots;
 	struct list_head pending_chunks;
-	struct list_head pending_ordered;
 	struct list_head switch_commits;
 	struct list_head dirty_bgs;
 	struct list_head io_bgs;
@@ -129,7 +130,6 @@ struct btrfs_trans_handle {
 	 */
 	struct btrfs_root *root;
 	struct seq_list delayed_ref_elem;
-	struct list_head ordered;
 	struct list_head qgroup_ref_list;
 	struct list_head new_bgs;
 };