Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 9ca9ee09 authored by Sage Weil's avatar Sage Weil Committed by Chris Mason
Browse files

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: default avatarSage 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: default avatarChris Mason <chris.mason@oracle.com>
parent 3117a773

fs/btrfs/ctree.h

+1 −0
Original line number Diff line number Diff line
@@ -518,6 +518,7 @@ struct btrfs_fs_info { 


	u64 generation;

	u64 last_trans_committed;

	u64 open_ioctl_trans;

	unsigned long mount_opt;

	u64 max_extent;

	u64 max_inline;

fs/btrfs/ioctl.c

+11 −1
Original line number Diff line number Diff line
@@ -715,7 +715,12 @@ long btrfs_ioctl_trans_start(struct file *file) 
		ret = -EINPROGRESS;

		goto out;

	}

	trans = btrfs_start_transaction(root, 0);



	mutex_lock(&root->fs_info->trans_mutex);

	root->fs_info->open_ioctl_trans++;

	mutex_unlock(&root->fs_info->trans_mutex);



	trans = btrfs_start_ioctl_transaction(root, 0);

	if (trans)

		file->private_data = trans;

	else
@@ -745,6 +750,11 @@ long btrfs_ioctl_trans_end(struct file *file) 
	}

	btrfs_end_transaction(trans, root);

	file->private_data = 0;



	mutex_lock(&root->fs_info->trans_mutex);

	root->fs_info->open_ioctl_trans--;

	mutex_unlock(&root->fs_info->trans_mutex);



out:

	return ret;

}

fs/btrfs/transaction.c

+13 −5
Original line number Diff line number Diff line
@@ -152,14 +152,14 @@ static void wait_current_trans(struct btrfs_root *root) 
}



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 *start_transaction(struct btrfs_root *root, 
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)

{
@@ -247,6 +254,7 @@ static void throttle_on_drops(struct btrfs_root *root) 
void btrfs_throttle(struct btrfs_root *root)

{

	mutex_lock(&root->fs_info->trans_mutex);

	if (!root->fs_info->open_ioctl_trans)

		wait_current_trans(root);

	mutex_unlock(&root->fs_info->trans_mutex);

fs/btrfs/transaction.h

+2 −0
Original line number Diff line number Diff line
@@ -83,6 +83,8 @@ struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root, 
						   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,