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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 942C6C43381 for ; Mon, 18 Mar 2019 17:25:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6BB0420854 for ; Mon, 18 Mar 2019 17:25:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727235AbfCRRZE (ORCPT ); Mon, 18 Mar 2019 13:25:04 -0400 Received: from foss.arm.com ([217.140.101.70]:38514 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726704AbfCRRZD (ORCPT ); Mon, 18 Mar 2019 13:25:03 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 37CCA1650; Mon, 18 Mar 2019 10:25:03 -0700 (PDT) Received: from e107155-lin (e107155-lin.cambridge.arm.com [10.1.196.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 683063F614; Mon, 18 Mar 2019 10:25:00 -0700 (PDT) Date: Mon, 18 Mar 2019 17:24:57 +0000 From: Sudeep Holla To: Oleg Nesterov Cc: x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Catalin Marinas , Will Deacon , Paul Mackerras , Michael Ellerman , Thomas Gleixner , Ingo Molnar , Richard Weinberger , jdike@addtoit.com, Steve Capper , Haibo Xu , Bin Lu , Andy Lutomirski Subject: Re: [PATCH v2 4/6] powerpc: use common ptrace_syscall_enter hook to handle _TIF_SYSCALL_EMU Message-ID: <20190318172457.GD18196@e107155-lin> References: <20190318104925.16600-1-sudeep.holla@arm.com> <20190318104925.16600-5-sudeep.holla@arm.com> <20190318172024.GB23521@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190318172024.GB23521@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 18, 2019 at 06:20:24PM +0100, Oleg Nesterov wrote: > On 03/18, Sudeep Holla wrote: > > > > --- a/arch/powerpc/kernel/ptrace.c > > +++ b/arch/powerpc/kernel/ptrace.c > > @@ -3278,35 +3278,29 @@ long do_syscall_trace_enter(struct pt_regs *regs) > > > > user_exit(); > > > > - flags = READ_ONCE(current_thread_info()->flags) & > > - (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE); > > - > > - if (flags) { > > - int rc = tracehook_report_syscall_entry(regs); > > + if (unlikely(ptrace_syscall_enter(regs))) { > > + /* > > + * A nonzero return code from tracehook_report_syscall_entry() > > + * tells us to prevent the syscall execution, but we are not > > + * going to execute it anyway. > > + * > > + * Returning -1 will skip the syscall execution. We want to > > + * avoid clobbering any registers, so we don't goto the skip > > + * label below. > > + */ > > + return -1; > > + } > > > > - if (unlikely(flags & _TIF_SYSCALL_EMU)) { > > - /* > > - * A nonzero return code from > > - * tracehook_report_syscall_entry() tells us to prevent > > - * the syscall execution, but we are not going to > > - * execute it anyway. > > - * > > - * Returning -1 will skip the syscall execution. We want > > - * to avoid clobbering any registers, so we don't goto > > - * the skip label below. > > - */ > > - return -1; > > - } > > + flags = READ_ONCE(current_thread_info()->flags) & _TIF_SYSCALL_TRACE; > > Why do we need READ_ONCE() with this change? > > And now that we change a single bit "flags" doesn't look like a good name. > > Again, to me this patch just makes the code look worse. Honestly, I don't > think that the new (badly named) ptrace_syscall_enter() hook makes any sense. > Worse because we end up reading current_thread_info->flags twice ? -- Regards, Sudeep