Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762987Ab3DCSFG (ORCPT ); Wed, 3 Apr 2013 14:05:06 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:46919 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762890Ab3DCSFE (ORCPT ); Wed, 3 Apr 2013 14:05:04 -0400 Date: Wed, 3 Apr 2013 19:04:43 +0100 From: Will Deacon To: Christopher Covington Cc: Catalin Marinas , "linux-arm-kernel@lists.infradead.org" , "linux-arm-msm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] arm64: Fix task tracing Message-ID: <20130403180443.GB21167@mudshark.cambridge.arm.com> References: <1365012061-31660-1-git-send-email-cov@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1365012061-31660-1-git-send-email-cov@codeaurora.org> 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 Content-Length: 1544 Lines: 45 Hi Christopher, On Wed, Apr 03, 2013 at 07:01:01PM +0100, Christopher Covington wrote: > For accurate accounting call contextidr_thread_switch before a > task is scheduled, rather than after. > > 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..c2cc249 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -311,11 +311,11 @@ struct task_struct *__switch_to(struct task_struct *prev, > fpsimd_thread_switch(next); > tls_thread_switch(next); > hw_breakpoint_thread_switch(next); > + contextidr_thread_switch(next); > > /* the actual thread switch */ > last = cpu_switch_to(prev, next); > > - contextidr_thread_switch(next); > return last; > } Catalin and I wondered about this and decided to go with the current approach in case a debugger, in response to the contextidr write, decided to go off and mine information about the *new* task using the sp. If we update the register before we've switched the registers, there's a sizeable window where the debugger will get confused. Do you have a real use-case that has triggered this patch? Cheers, Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/