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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A1C33C48BE4 for ; Thu, 25 Aug 2022 13:32:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=V6dHO6+9zigQVqyoWD/BUYkyT2eavjM9m4KSXKP3Bcw=; b=vt+LpMNo4FY4mo 8aQdOtAuoZnxOva1jL8LU0jHye32B8zYOC4f9QKcQXcvB3u/pJMHW5i65xMziCkbbcRosmceHtyQv 3klyTyiThOhUw2jk0y3SiNMGxUdrJKVKCN7lWjJPrLEtCaLQaUaqpQtyYZL8QZQ+9K7WYvHz5mCGS LimLWnYQfTVhZxDoQKCPN4xGPBAilV58E0TYU2T4mXlTzHx07a9OcDQ6HWGCD8LdjhwIlnp5LKueA 8ug2fCLRb27q/JwQDJQSHQiZjnwn7FdzN88BeU/exk6iRm+JD7c/NFCX8XRuD1KDE824zZVRL/KCi XBWtIOFDHmL/ldvzTtHQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oRCwq-00Eoyz-RW; Thu, 25 Aug 2022 13:31:05 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oRCvl-00EoKP-Q2 for linux-arm-kernel@lists.infradead.org; Thu, 25 Aug 2022 13:30:00 +0000 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 CF31BD6E; Thu, 25 Aug 2022 06:29:59 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.47.11]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 08F6B3F71A; Thu, 25 Aug 2022 06:29:53 -0700 (PDT) Date: Thu, 25 Aug 2022 14:29:51 +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 1/2] arm64/traps: Replace this_cpu_* with raw_cpu_* in panic_bad_stack() Message-ID: References: <20220825063154.69-1-thunder.leizhen@huawei.com> <20220825063154.69-2-thunder.leizhen@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220825063154.69-2-thunder.leizhen@huawei.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220825_062957_941661_4A6AFC00 X-CRM114-Status: GOOD ( 23.21 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Aug 25, 2022 at 02:31:53PM +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, before > commit 8168f098867f ("arm64: entry: split bad stack entry"), the operation > this_cpu_read() precedes arm64_enter_nmi(). If set_preempt_need_resched() > is called before stack overflow, this_cpu_read() may trigger scheduling, > see pseudocode below. > > Pseudocode of this_cpu_read(xx) when CONFIG_PREEMPTION=y: > preempt_disable_notrace(); > raw_cpu_read(xx); > if (unlikely(__preempt_count_dec_and_test())) > __preempt_schedule_notrace(); Ok, but in mainline we have commit 8168f098867f; so we cannot reach here without having fiddled with the preempt count. Are you saying that some stable kernel is broken because it lacks commit 8168f098867f? Is so, I think the right fix is to backport commit 8168f098867f, and that is then irrelevant to this change. > 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'm happy to use raw_cpu_*() here, to minimize the work we have to do, any any risks with e.g. instrumentation, but as above I don't think the case mentioned in the commit message is relevant. Thanks, Mark. > > Signed-off-by: Zhen Lei > --- > arch/arm64/kernel/traps.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > index b7fed33981f7b76..e6b6f4650e3d895 100644 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -871,8 +871,8 @@ DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack) > void panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigned long far) > { > unsigned long tsk_stk = (unsigned long)current->stack; > - unsigned long irq_stk = (unsigned long)this_cpu_read(irq_stack_ptr); > - unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack); > + unsigned long irq_stk = (unsigned long)raw_cpu_read(irq_stack_ptr); > + unsigned long ovf_stk = (unsigned long)raw_cpu_ptr(overflow_stack); > > console_verbose(); > pr_emerg("Insufficient stack space to handle exception!"); > -- > 2.25.1 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel