From 42383020beb1cfb05f5d330cc311931bc4917a97 Mon Sep 17 00:00:00 2001 From: Sage Weil Date: Fri, 26 Sep 2014 08:30:06 -0700 Subject: [PATCH] Btrfs: fix race in WAIT_SYNC ioctl We check whether transid is already committed via last_trans_committed and then search through trans_list for pending transactions. If last_trans_committed is updated by btrfs_commit_transaction after we check it (there is no locking), we will fail to find the committed transaction and return EINVAL to the caller. This has been observed occasionally by ceph-osd (which uses this ioctl heavily). Fix by rechecking whether the provided transid <= last_trans_committed after the search fails, and if so return 0. Signed-off-by: Sage Weil Signed-off-by: Chris Mason --- fs/btrfs/transaction.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index a47b100..86ef8d7 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -609,7 +609,6 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid) if (transid <= root->fs_info->last_trans_committed) goto out; - ret = -EINVAL; /* find specified transaction */ spin_lock(&root->fs_info->trans_lock); list_for_each_entry(t, &root->fs_info->trans_list, list) { @@ -625,9 +624,16 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid) } } spin_unlock(&root->fs_info->trans_lock); - /* The specified transaction doesn't exist */ - if (!cur_trans) + + /* + * The specified transaction doesn't exist, or we + * raced with btrfs_commit_transaction + */ + if (!cur_trans) { + if (transid > root->fs_info->last_trans_committed) + ret = -EINVAL; goto out; + } } else { /* find newest transaction that is committing | committed */ spin_lock(&root->fs_info->trans_lock); -- 2.7.4