From 9ca9ee09c176a814189063c8b88f75c8f8e4ad19 Mon Sep 17 00:00:00 2001 From: Sage Weil Date: Mon, 4 Aug 2008 10:41:27 -0400 Subject: 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 --- ctree.h | 1 + ioctl.c | 12 +++++++++++- transaction.c | 18 +++++++++++++----- transaction.h | 2 ++ 4 files changed, 27 insertions(+), 6 deletions(-) Signed-off-by: Chris Mason --- fs/btrfs/transaction.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'fs/btrfs/transaction.c') diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index cf73342e8215..a2c821e3c3a7 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -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) { @@ -247,7 +254,8 @@ harder: 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); -- cgit v1.2.3