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 07318C77B73 for ; Tue, 30 May 2023 09:46:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229615AbjE3Jqj (ORCPT ); Tue, 30 May 2023 05:46:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57142 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229701AbjE3Jqg (ORCPT ); Tue, 30 May 2023 05:46:36 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 1EAC0EC for ; Tue, 30 May 2023 02:46:35 -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 192C92F4; Tue, 30 May 2023 02:47:20 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.25.100]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 199643F663; Tue, 30 May 2023 02:46:32 -0700 (PDT) Date: Tue, 30 May 2023 10:46:27 +0100 From: Mark Rutland To: Eric Chan Cc: Catalin Marinas , Will Deacon , "Paul E . McKenney" , Mark Brown , Frederic Weisbecker , Mukesh Ojha , Josh Poimboeuf , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: Fix 'lock held when returning to user space' lockdep warning Message-ID: References: <20230526184823.1230974-1-ericchancf@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230526184823.1230974-1-ericchancf@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Eric, The subject line for this patch is misleading, as it makes it sound like we're currently hitting a warning of the form: lock held when returning to user space ... when in actuality this patch is *adding* support for that warning. This is a missing feature, not a fix (and e.g. doesn't require backporting to stable). On Fri, May 26, 2023 at 06:48:23PM +0000, Eric Chan wrote: > The arm64 architecture lacks support for CONFIG_GENERIC_ENTRY, resulting > in the failure to report the lockdep warning > "lock held when returning to user space" when lockdep is enabled. > > Rename the function to align with exit_to_user_mode_prepare in > kernel/entry/common.c to improve readability. Considering the point about the commit title, could you please reword this to be clear that we're adding support for a feature, rather than fixing something that's broken, e.g. | arm64: lockdep: enable checks for held locks when returning to userspace | | Currently arm64 doesn't use CONFIG_GENERIC_ENTRY and doesn't call | lockdep_sys_exit() when returning to userspace. This means that lockdep won't | check for held locks when returning to userspace, which would be useful to | detect kernel bugs. | | Call lockdep_sys_exit() when returning to userspace, enabling checking for | held locks. | | At the same time, rename arm64's prepare_exit_to_user_mode() to | exit_to_user_mode_prepare() to more clearly align with the naming in the | generic entry code. With that wording: Acked-by: Mark Rutland Thanks, Mark. > Signed-off-by: Eric Chan > --- > arch/arm64/kernel/entry-common.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c > index 3af3c01c93a6..9d6827201b6c 100644 > --- a/arch/arm64/kernel/entry-common.c > +++ b/arch/arm64/kernel/entry-common.c > @@ -126,7 +126,7 @@ static __always_inline void __exit_to_user_mode(void) > lockdep_hardirqs_on(CALLER_ADDR0); > } > > -static __always_inline void prepare_exit_to_user_mode(struct pt_regs *regs) > +static __always_inline void exit_to_user_mode_prepare(struct pt_regs *regs) > { > unsigned long flags; > > @@ -135,11 +135,13 @@ static __always_inline void prepare_exit_to_user_mode(struct pt_regs *regs) > flags = read_thread_flags(); > if (unlikely(flags & _TIF_WORK_MASK)) > do_notify_resume(regs, flags); > + > + lockdep_sys_exit(); > } > > static __always_inline void exit_to_user_mode(struct pt_regs *regs) > { > - prepare_exit_to_user_mode(regs); > + exit_to_user_mode_prepare(regs); > mte_check_tfsr_exit(); > __exit_to_user_mode(); > } > -- > 2.41.0.rc0.172.g3f132b7071-goog >