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Commit 42383020 authored by Sage Weil's avatar Sage Weil Committed by Chris Mason
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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: default avatarSage Weil <sage@redhat.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
parent 656f30db

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);