Hit this nice little deadlock. What happens is this
__btrfs_end_transaction with throttle set, --use_count so it equals 0
btrfs_commit_transaction
<somebody else actually manages to start the commit>
btrfs_end_transaction --use_count so now its -1 <== BAD
we just return and wait on the transaction
This is bad because we just return after our use_count is -1 and don't let go
of our num_writer count on the transaction, so the guy committing the
transaction just sits there forever. Fix this by inc'ing our use_count if we're
going to call commit_transaction so that if we call btrfs_end_transaction it's
valid. Thanks,
Signed-off-by: Josef Bacik <josef@xxxxxxxxxx>
---
fs/btrfs/transaction.c | 13 ++++++++++---
1 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 654755b..00b81fb5 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -497,10 +497,17 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
}
if (lock && cur_trans->blocked && !cur_trans->in_commit) {
- if (throttle)
+ if (throttle) {
+ /*
+ * We may race with somebody else here so end up having
+ * to call end_transaction on ourselves again, so inc
+ * our use_count.
+ */
+ trans->use_count++;
return btrfs_commit_transaction(trans, root);
- else
+ } else {
wake_up_process(info->transaction_kthread);
+ }
}
WARN_ON(cur_trans != info->running_transaction);
@@ -1225,7 +1232,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
if (cur_trans->in_commit) {
spin_unlock(&cur_trans->commit_lock);
atomic_inc(&cur_trans->use_count);
- btrfs_end_transaction(trans, root);
+ __btrfs_end_transaction(trans, root, 0, 1);
ret = wait_for_commit(root, cur_trans);
BUG_ON(ret);
--
1.7.5.2
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