[LukeShu]

The argv array (and the envp array) are in a page the kernel set up when it created the process, and the kernel holds on a reference to it, and remembers the addres of those arrays in the page. The kernel doesn't need to "watch" that memory, when you read from `/proc/$pid/cmdline` or `/proc/$pid/environ`, procfs literally reads directly from $pid's memory space (remember that the kernel controls the page table, it can look in to the memory space of any process it wants to). The kernel doesn't "know" that the value changed, it just reads the current value from process' memory.