From 9ca9ee09c176a814189063c8b88f75c8f8e4ad19 Mon Sep 17 00:00:00 2001 From: Sage Weil Date: Mon, 4 Aug 2008 10:41:27 -0400 Subject: [PATCH] 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/ctree.h | 1 + fs/btrfs/ioctl.c | 12 +++++++++++- fs/btrfs/transaction.c | 18 +++++++++++++----- fs/btrfs/transaction.h | 2 ++ 4 files changed, 27 insertions(+), 6 deletions(-) diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 9b025960bbde..62499dd761b7 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -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; diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 224da287b3ed..0b63c3c77cfd 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -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; } 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); diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h index f5adb23151fb..2c73caeebb2c 100644 --- a/fs/btrfs/transaction.h +++ b/fs/btrfs/transaction.h @@ -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, -- 2.20.1