How is Code in do_sys_settimeofday() safe in case of SMP and Nest Kernel Path?

["Dong Feng" <middle.fengdong@gmail.com>]

Hi, all,

I got a question, that is, I am confused by the following code in
do_sys_settimeofday().

if (tz) {
    /* SMP safe, global irq locking makes it work. */
        sys_tz = *tz;
        if (firsttime) {
            firsttime = 0;
            if (!tv)
                warp_clock();
    }
}


For my understanding, an assignment between structs should be a
bit-wise copy. Such operation is not atomic, so it can not be supposed
SMP-safe. And the subsequent test-and-assign operation on firsttime is
not atomic, either.

If the comments mean the subsequent code is SMP-safe and can prevent
nest-kernel-path, how does it achieves that?

Thank you in advance.
Feng,Dong