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Message-ID: <Pine.LNX.4.64.0609290903550.23840@schroedinger.engr.sgi.com>
Date: Fri, 29 Sep 2006 09:05:57 -0700 (PDT)
From: Christoph Lameter <clameter@....com>
To: Dong Feng <middle.fengdong@...il.com>
cc: Andi Kleen <ak@...e.de>, Nick Piggin <nickpiggin@...oo.com.au>,
Arjan van de Ven <arjan@...radead.org>,
Paul Mackerras <paulus@...ba.org>,
David Howells <dhowells@...hat.com>,
linux-kernel@...r.kernel.org
Subject: Re: How is Code in do_sys_settimeofday() safe in case of SMP and
Nest Kernel Path?
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.
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