Btrfs: fix ioctl-initiated transactions vs wait_current_trans()
Commit 597:466b27332893 (btrfs_start_transaction: wait for commits in
progress) breaks the transaction start/stop ioctls by making
btrfs_start_transaction conditionally wait for the next transaction to
start. If an application artificially is holding a transaction open,
things deadlock.
This workaround maintains a count of open ioctl-initiated transactions in
fs_info, and avoids wait_current_trans() if any are currently open (in
start_transaction() and btrfs_throttle()). The start transaction ioctl
uses a new btrfs_start_ioctl_transaction() that _does_ call
wait_current_trans(), effectively pushing the join/wait decision to the
outer ioctl-initiated transaction.
This more or less neuters btrfs_throttle() when ioctl-initiated
transactions are in use, but that seems like a pretty fundamental
consequence of wrapping lots of write()'s in a transaction. Btrfs has no
way to tell if the application considers a given operation as part of it's
transaction.
Obviously, if the transaction start/stop ioctls aren't being used, there
is no effect on current behavior.
Signed-off-by: Sage Weil <sage@newdream.net>
---
ctree.h | 1 +
ioctl.c | 12 +++++++++++-
transaction.c | 18 +++++++++++++-----
transaction.h | 2 ++
4 files changed, 27 insertions(+), 6 deletions(-)
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index f5adb23..2c73caee 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -83,6 +83,8 @@
int num_blocks);
struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root,
int num_blocks);
+struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *r,
+ 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,