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.c b/fs/btrfs/transaction.c
index cf73342..a2c821e 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -152,14 +152,14 @@
}
struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
- int num_blocks, int join)
+ int num_blocks, int wait)
{
struct btrfs_trans_handle *h =
kmem_cache_alloc(btrfs_trans_handle_cachep, GFP_NOFS);
int ret;
mutex_lock(&root->fs_info->trans_mutex);
- if (!join)
+ if ((wait == 1 && !root->fs_info->open_ioctl_trans) || wait == 2)
wait_current_trans(root);
ret = join_transaction(root);
BUG_ON(ret);
@@ -180,14 +180,21 @@
struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
int num_blocks)
{
- return start_transaction(root, num_blocks, 0);
+ return start_transaction(root, num_blocks, 1);
}
struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root,
int num_blocks)
{
- return start_transaction(root, num_blocks, 1);
+ return start_transaction(root, num_blocks, 0);
}
+struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *r,
+ int num_blocks)
+{
+ return start_transaction(r, num_blocks, 2);
+}
+
+
static noinline int wait_for_commit(struct btrfs_root *root,
struct btrfs_transaction *commit)
{
@@ -247,7 +254,8 @@
void btrfs_throttle(struct btrfs_root *root)
{
mutex_lock(&root->fs_info->trans_mutex);
- wait_current_trans(root);
+ if (!root->fs_info->open_ioctl_trans)
+ wait_current_trans(root);
mutex_unlock(&root->fs_info->trans_mutex);
throttle_on_drops(root);