From: Jia-Ju Bai <baijiaju1990@xxxxxxxxx> commit 168a2f776b9762f4021421008512dd7ab7474df1 upstream. In btrfs_get_root_ref(), when btrfs_insert_fs_root() fails, btrfs_put_root() can happen for two reasons: - the root already exists in the tree, in that case it returns the reference obtained in btrfs_lookup_fs_root() - another error so the cleanup is done in the fail label Calling btrfs_put_root() unconditionally would lead to double decrement of the root reference possibly freeing it in the second case. Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx> Fixes: bc44d7c4b2b1 ("btrfs: push btrfs_grab_fs_root into btrfs_get_fs_root") CC: stable@xxxxxxxxxxxxxxx # 5.10+ Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx> Reviewed-by: David Sterba <dsterba@xxxxxxxx> Signed-off-by: David Sterba <dsterba@xxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/btrfs/disk-io.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -1596,9 +1596,10 @@ again: ret = btrfs_insert_fs_root(fs_info, root); if (ret) { - btrfs_put_root(root); - if (ret == -EEXIST) + if (ret == -EEXIST) { + btrfs_put_root(root); goto again; + } goto fail; } return root; Patches currently in stable-queue which might be from baijiaju1990@xxxxxxxxx are queue-5.10/btrfs-fix-root-ref-counts-in-error-handling-in-btrfs_get_root_ref.patch