From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Tue, 29 Jul 2014 20:46:07 +0200 (CEST) Received: from mx1.redhat.com ([209.132.183.28]:20160 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6816676AbaG2SqEGPIbc (ORCPT ); Tue, 29 Jul 2014 20:46:04 +0200 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s6TIjr0l025292 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 29 Jul 2014 14:45:54 -0400 Received: from tranklukator.brq.redhat.com (dhcp-1-191.brq.redhat.com [10.34.1.191]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id s6TIjoab032482; Tue, 29 Jul 2014 14:45:51 -0400 Received: by tranklukator.brq.redhat.com (nbSMTP-1.00) for uid 500 oleg@redhat.com; Tue, 29 Jul 2014 20:44:14 +0200 (CEST) Date: Tue, 29 Jul 2014 20:44:11 +0200 From: Oleg Nesterov To: Andy Lutomirski Cc: "linux-kernel@vger.kernel.org" , Kees Cook , Will Drewry , X86 ML , "linux-arm-kernel@lists.infradead.org" , Linux MIPS Mailing List , linux-arch , LSM List , Alexei Starovoitov , "H. Peter Anvin" Subject: Re: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases Message-ID: <20140729184411.GA6035@redhat.com> References: <3f649f5658a163645e3ce15156176c325283762e.1405992946.git.luto@amacapital.net> <20140728173723.GA20993@redhat.com> <20140729165416.GA967@redhat.com> <20140729173136.GA2808@redhat.com> <20140729181615.GA4950@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 41797 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: oleg@redhat.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On 07/29, Andy Lutomirski wrote: > > On Tue, Jul 29, 2014 at 11:16 AM, Oleg Nesterov wrote: > > On 07/29, Andy Lutomirski wrote: > >> > >> On Tue, Jul 29, 2014 at 10:31 AM, Oleg Nesterov wrote: > >> > > >> > TIF_NOHZ is set if and only if context_tracking_is_enabled() is true. > >> > So I think that > >> > > >> > work = current_thread_info()->flags & (_TIF_WORK_SYSCALL_ENTRY & ~TIF_NOHZ); > >> > > >> > user_exit(); > >> > > >> > looks a bit better. But I won't argue. > >> > >> I don't get it. > > > > Don't worry, you are not alone. > > > >> context_tracking_is_enabled is global, and TIF_NOHZ > >> is per-task. Isn't this stuff determined per-task or per-cpu or > >> something? > >> > >> IOW, if one CPU is running something that's very heavily > >> userspace-oriented and another CPU is doing something syscall- or > >> sleep-heavy, then shouldn't only the first CPU end up paying the price > >> of context tracking? > > > > Please see another email I sent to Frederic. > > > I'll add at least this argument in favor of my approach: if context > tracking works at all, then it had better not demand that syscall > entry call user_exit if TIF_NOHZ is *not* set. I disagree. At least I disagree with that you should enforce this in syscall_trace_enter() paths, and in any case this has nothing to do with these changes. But again, I won't insist, so please forget. > So adding the > condition ought to be safe, barring dumb bugs in my code. Yes, I think it is technically correct. Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com ([209.132.183.28]:20160 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6816676AbaG2SqEGPIbc (ORCPT ); Tue, 29 Jul 2014 20:46:04 +0200 Date: Tue, 29 Jul 2014 20:44:11 +0200 From: Oleg Nesterov Subject: Re: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases Message-ID: <20140729184411.GA6035@redhat.com> References: <3f649f5658a163645e3ce15156176c325283762e.1405992946.git.luto@amacapital.net> <20140728173723.GA20993@redhat.com> <20140729165416.GA967@redhat.com> <20140729173136.GA2808@redhat.com> <20140729181615.GA4950@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Return-Path: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Andy Lutomirski Cc: "linux-kernel@vger.kernel.org" , Kees Cook , Will Drewry , X86 ML , "linux-arm-kernel@lists.infradead.org" , Linux MIPS Mailing List , linux-arch , LSM List , Alexei Starovoitov , "H. Peter Anvin" Message-ID: <20140729184411.fTYWJWCHdV5aydw9kxGf6iLii4hQrUuZkH4tBJtfFmA@z> On 07/29, Andy Lutomirski wrote: > > On Tue, Jul 29, 2014 at 11:16 AM, Oleg Nesterov wrote: > > On 07/29, Andy Lutomirski wrote: > >> > >> On Tue, Jul 29, 2014 at 10:31 AM, Oleg Nesterov wrote: > >> > > >> > TIF_NOHZ is set if and only if context_tracking_is_enabled() is true. > >> > So I think that > >> > > >> > work = current_thread_info()->flags & (_TIF_WORK_SYSCALL_ENTRY & ~TIF_NOHZ); > >> > > >> > user_exit(); > >> > > >> > looks a bit better. But I won't argue. > >> > >> I don't get it. > > > > Don't worry, you are not alone. > > > >> context_tracking_is_enabled is global, and TIF_NOHZ > >> is per-task. Isn't this stuff determined per-task or per-cpu or > >> something? > >> > >> IOW, if one CPU is running something that's very heavily > >> userspace-oriented and another CPU is doing something syscall- or > >> sleep-heavy, then shouldn't only the first CPU end up paying the price > >> of context tracking? > > > > Please see another email I sent to Frederic. > > > I'll add at least this argument in favor of my approach: if context > tracking works at all, then it had better not demand that syscall > entry call user_exit if TIF_NOHZ is *not* set. I disagree. At least I disagree with that you should enforce this in syscall_trace_enter() paths, and in any case this has nothing to do with these changes. But again, I won't insist, so please forget. > So adding the > condition ought to be safe, barring dumb bugs in my code. Yes, I think it is technically correct. Oleg.