From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Thu, 24 Sep 2009 17:50:22 +0200 (CEST) Received: from h5.dl5rb.org.uk ([81.2.74.5]:57672 "EHLO h5.dl5rb.org.uk" rhost-flags-OK-OK-OK-OK) by ftp.linux-mips.org with ESMTP id S1492630AbZIXPuP (ORCPT ); Thu, 24 Sep 2009 17:50:15 +0200 Received: from h5.dl5rb.org.uk (localhost.localdomain [127.0.0.1]) by h5.dl5rb.org.uk (8.14.3/8.14.3) with ESMTP id n8OFpU2A013512; Thu, 24 Sep 2009 16:51:30 +0100 Received: (from ralf@localhost) by h5.dl5rb.org.uk (8.14.3/8.14.3/Submit) id n8OFpTZX013510; Thu, 24 Sep 2009 16:51:29 +0100 Date: Thu, 24 Sep 2009 16:51:29 +0100 From: Ralf Baechle To: Randy MacLeod Cc: linux-mips@linux-mips.org Subject: Re: MIPS: [raw_]smp_processor_id uses current_thread_info Message-ID: <20090924155129.GA11576@linux-mips.org> References: <21f828e90909231127h70f69047v91b9261226681d53@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <21f828e90909231127h70f69047v91b9261226681d53@mail.gmail.com> User-Agent: Mutt/1.5.19 (2009-01-05) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 24092 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ralf@linux-mips.org Precedence: bulk X-list: linux-mips On Wed, Sep 23, 2009 at 02:27:26PM -0400, Randy MacLeod wrote: > I'd like advice on changing the implementation of smp_processor_id on > Cavium specifically and/or MIPS generally. > > Currently we have: arch/mips/include/asm/smp.h > #define raw_smp_processor_id() (current_thread_info()->cpu) > > A co-worker has an issue where the current thread pointer is corrupted > on a Cavium MIPS system running 2.6.14 (but the same code exists in 2.6.31). > During the resulting panic() the kernel calls smp_processor_id() > which dereferences the corrupt task pointer again - ouch. I've notice that > other arches have raw_smp_processor_id() defined to > - a platform specific register read, or > - a percpu variable or > - have a hard_smp_processor_id() defined > This last one is presumably for times when you don't trust the kernel > data structures to be > sane. Dereferencing current_thread_info()->cpu is fairly likely to hit in the cache so probably a single cycle operation. raw_smp_processor_id() is also a very common operation so you really don't want to change it to something slower except for a debugging kernel. If you have a good kernel stack pointer you can compute the thread pointer from that: ori $28, sp, _THREAD_MASK xori $28, _THREAD_MASK > I can create a patch that calls cvmx_get_core_num(); for cavium. > Is there a more generic way to get the cpu number on MIPS? raw_smp_processor_id() returns the processor ID as counted by Linux. That number does not necessarily match the firmware's numbering. Ralf