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

Dong Feng
2006-09-29T16:16:12Z

2006/9/30, Christoph Lameter <clameter@sgi.com>:
> On Fri, 29 Sep 2006, Dong Feng wrote:
>
> > For my understanding, an assignment between structs should be a
> > bit-wise copy. Such operation is not atomic, so it can not be supposed
>
> Byte or Machine word yes.
>
> > SMP-safe. And the subsequent test-and-assign operation on firsttime is
> > not atomic, either.
>
> No its not atomic on its own. Correct.
>
> > If the comments mean the subsequent code is SMP-safe and can prevent
> > nest-kernel-path, how does it achieves that?
>
> It relies on locking outside of do_sys_settimeofday(). Seems that this
> indicates locking is to be performed by the arch before calling
> do_sys_settimeofday. Looks suspicious to me. Check that this function is
> always called with the same lock.
>

Yes, that is the question. The whole invocation path is
sys_settimeofday() -> do_sys_settimeofday()

I do not find a lock embracing do_sys_settimeofday().

Moreover, seems neither write operations nor read operations on sys_tz
is protected by any locks, in sys_gettimeofday() and
sys_settimeofday() respectively.