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

From: Dong Feng
Date: Fri Sep 29 2006 - 12:16:29 EST

2006/9/30, Christoph Lameter <clameter@xxxxxxx>:
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.
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