From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755818Ab3DOKqE (ORCPT ); Mon, 15 Apr 2013 06:46:04 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:53060 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755700Ab3DOKqC (ORCPT ); Mon, 15 Apr 2013 06:46:02 -0400 Date: Mon, 15 Apr 2013 11:45:42 +0100 From: Will Deacon To: Catalin Marinas Cc: Christopher Covington , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-arm-msm@vger.kernel.org" Subject: Re: [PATCH v2] arm64: Fix task tracing Message-ID: <20130415104542.GE9827@mudshark.cambridge.arm.com> References: <20130408153132.GQ17476@mudshark.cambridge.arm.com> <1365510814-21343-1-git-send-email-cov@codeaurora.org> <20130415101159.GA25095@localhost.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130415101159.GA25095@localhost.cambridge.arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 15, 2013 at 11:11:59AM +0100, Catalin Marinas wrote: > On Tue, Apr 09, 2013 at 01:33:34PM +0100, Christopher Covington wrote: > > For accurate accounting pass contextidr_thread_switch the prev > > task pointer, since cpu_switch_to has at that point changed the > > the stack pointer. > > > > Signed-off-by: Christopher Covington > > --- > > arch/arm64/kernel/process.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > index 0337cdb..a49b25a 100644 > > --- a/arch/arm64/kernel/process.c > > +++ b/arch/arm64/kernel/process.c > > @@ -315,7 +315,7 @@ struct task_struct *__switch_to(struct task_struct *prev, > > /* the actual thread switch */ > > last = cpu_switch_to(prev, next); > > > > - contextidr_thread_switch(next); > > + contextidr_thread_switch(prev); > > The original code was indeed wrong but using prev isn't any better. For > a newly created thread, prev is probably 0 (if it's in a register, > cpu_context has been zeroed by copy_thread()) or some random stack > value. Really? If prev is NULL in context_switch(...), the scheduler will implode, and I can't see where else switch_to is called from. Which code path are you thinking of? Will