Btrfs: fix race in WAIT_SYNC ioctl (42383020) · Commits · 戴 / test

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 <sage@redhat.com> Signed-off-by:

Chris Mason <clm@fb.com>

fs/btrfs/transaction.c

+9 −3

Original line number	Diff line number	Diff line
		@@ -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);

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