From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1106CC64990 for ; Thu, 25 Aug 2022 13:34:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242803AbiHYNe0 (ORCPT ); Thu, 25 Aug 2022 09:34:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38994 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240693AbiHYNeH (ORCPT ); Thu, 25 Aug 2022 09:34:07 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3C14DB7280 for ; Thu, 25 Aug 2022 06:33:09 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6ABA3D6E; Thu, 25 Aug 2022 06:32:52 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.47.11]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 902443F71A; Thu, 25 Aug 2022 06:32:46 -0700 (PDT) Date: Thu, 25 Aug 2022 14:32:43 +0100 From: Mark Rutland To: Zhen Lei Cc: Catalin Marinas , Will Deacon , Russell King , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, patches@armlinux.org.uk Subject: Re: [PATCH 2/2] ARM: Replace this_cpu_* with raw_cpu_* in panic_bad_stack() Message-ID: References: <20220825063154.69-1-thunder.leizhen@huawei.com> <20220825063154.69-3-thunder.leizhen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220825063154.69-3-thunder.leizhen@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 25, 2022 at 02:31:54PM +0800, Zhen Lei wrote: > The hardware automatically disable the IRQ interrupt before jumping to the > interrupt or exception vector. Therefore, the preempt_disable() operation > in this_cpu_read() after macro expansion is unnecessary. In fact, function > this_cpu_read() may trigger scheduling, see pseudocode below. > > Pseudocode of this_cpu_read(xx): > preempt_disable_notrace(); > raw_cpu_read(xx); > if (unlikely(__preempt_count_dec_and_test())) > __preempt_schedule_notrace(); > > Therefore, use raw_cpu_* instead of this_cpu_* to eliminate potential > hazards. At the very least, it reduces a few lines of assembly code. I think if scheduling is a problem here, something should increment the preempt_count as is done on arm64, since any other operation in this function could end up causing preemption. Regardless, I also think it's sensible to use raw_cpu_*() here, but I don't think that actually fixes the problem the commit message describes. Thanks, Mark. > > Signed-off-by: Zhen Lei > --- > KernelVersion: v6.0-rc2 > arch/arm/kernel/traps.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c > index 1518a1f443ff866..d5903d790cf3b7e 100644 > --- a/arch/arm/kernel/traps.c > +++ b/arch/arm/kernel/traps.c > @@ -927,9 +927,9 @@ asmlinkage void handle_bad_stack(struct pt_regs *regs) > { > unsigned long tsk_stk = (unsigned long)current->stack; > #ifdef CONFIG_IRQSTACKS > - unsigned long irq_stk = (unsigned long)this_cpu_read(irq_stack_ptr); > + unsigned long irq_stk = (unsigned long)raw_cpu_read(irq_stack_ptr); > #endif > - unsigned long ovf_stk = (unsigned long)this_cpu_read(overflow_stack_ptr); > + unsigned long ovf_stk = (unsigned long)raw_cpu_read(overflow_stack_ptr); > > console_verbose(); > pr_emerg("Insufficient stack space to handle exception!"); > -- > 2.25.1 >