check

    fn check(b: *Bucket, s: *SafeAllocator) void {
        var footer = b.lastAlloc(s, b.fill).?;
        while (true) {
            const modify = @atomicLoad(
                AllocFooter.Modify,
                &footer.modify,
                // The only possible value should be `.freed` since `b.alloc_count`
                // has been loaded with `.acquire`. However, another thread may be trying to
                // modify the allocation after it is freed and so the other thread is going
                // to panic even if this thread still sees `.freed`.
                .unordered,
            ).storedXor(&footer.modify);
            if (modify != .freed or footer.actualChecksum(s) != footer.checksum ^ s.canary) {
                panic("corrupted footer metadata in bucket at *{x}", .{@intFromPtr(&footer)});
            }

            s.checkFreed(footer);
            footer = footer.bucketPrev(b, s) orelse break;
        }
    }