Btrfs: protect the pending_snapshots list with trans_lock

Currently there is nothing protecting the pending_snapshots list on the
transaction.  We only hold the directory mutex that we are snapshotting and a
read lock on the subvol_sem, so we could race with somebody else creating a
snapshot in a different directory and end up with list corruption.  So protect
this list with the trans_lock.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index b793d112d1f6..a3c4751e07db 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -482,8 +482,10 @@ static int create_snapshot(struct btrfs_root *root, struct dentry *dentry,
         ret = btrfs_snap_reserve_metadata(trans, pending_snapshot);
         BUG_ON(ret);
 
+        spin_lock(&root->fs_info->trans_lock);
         list_add(&pending_snapshot->list,
                  &trans->transaction->pending_snapshots);
+        spin_unlock(&root->fs_info->trans_lock);
         if (async_transid) {
                 *async_transid = trans->transid;
                 ret = btrfs_commit_transaction_async(trans,