From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules Date: Sun, 7 Apr 2019 16:41:36 -0400 (EDT) Message-ID: <1632568795.549.1554669696728.JavaMail.zimbra@efficios.com> References: <20190402142816.GA13084@linux.ibm.com> <20190403162039.GA14111@linux.ibm.com> <20190405232835.GA24702@linux.ibm.com> <20190406230613.GA187766@google.com> <20190407133941.GC14111@linux.ibm.com> <20190407135937.GA30053@linux.ibm.com> <134026717.535.1554665176677.JavaMail.zimbra@efficios.com> <20190407193202.GA30934@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190407193202.GA30934@localhost> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: "Joel Fernandes, Google" Cc: David Howells , amd-gfx , linux-nvdimm , Peter Zijlstra , fweisbec , dri-devel , Lai Jiangshan , linux-kernel , rostedt , Josh Triplett , rcu , Eric Dumazet , Thomas Gleixner , Oleg Nesterov , dipankar , Andrew Morton , paulmck , Ingo Molnar List-Id: linux-nvdimm@lists.01.org ----- On Apr 7, 2019, at 3:32 PM, Joel Fernandes, Google joel-QYYGw3jwrUn5owFQY34kdNi2O/JbrIOy@public.gmane.org wrote: > On Sun, Apr 07, 2019 at 03:26:16PM -0400, Mathieu Desnoyers wrote: >> ----- On Apr 7, 2019, at 9:59 AM, paulmck paulmck-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org wrote: >> >> > On Sun, Apr 07, 2019 at 06:39:41AM -0700, Paul E. McKenney wrote: >> >> On Sat, Apr 06, 2019 at 07:06:13PM -0400, Joel Fernandes wrote: >> > >> > [ . . . ] >> > >> >> > > diff --git a/include/asm-generic/vmlinux.lds.h >> >> > > b/include/asm-generic/vmlinux.lds.h >> >> > > index f8f6f04c4453..c2d919a1566e 100644 >> >> > > --- a/include/asm-generic/vmlinux.lds.h >> >> > > +++ b/include/asm-generic/vmlinux.lds.h >> >> > > @@ -338,6 +338,10 @@ >> >> > > KEEP(*(__tracepoints_ptrs)) /* Tracepoints: pointer array */ \ >> >> > > __stop___tracepoints_ptrs = .; \ >> >> > > *(__tracepoints_strings)/* Tracepoints: strings */ \ >> >> > > + . = ALIGN(8); \ >> >> > > + __start___srcu_struct = .; \ >> >> > > + *(___srcu_struct_ptrs) \ >> >> > > + __end___srcu_struct = .; \ >> >> > > } \ >> >> > >> >> > This vmlinux linker modification is not needed. I tested without it and srcu >> >> > torture works fine with rcutorture built as a module. Putting further prints >> >> > in kernel/module.c verified that the kernel is able to find the srcu structs >> >> > just fine. You could squash the below patch into this one or apply it on top >> >> > of the dev branch. >> >> >> >> Good point, given that otherwise FORTRAN named common blocks would not >> >> work. >> >> >> >> But isn't one advantage of leaving that stuff in the RO_DATA_SECTION() >> >> macro that it can be mapped read-only? Or am I suffering from excessive >> >> optimism? >> > >> > And to answer the other question, in the case where I am suffering from >> > excessive optimism, it should be a separate commit. Please see below >> > for the updated original commit thus far. >> > >> > And may I have your Tested-by? >> >> Just to confirm: does the cleanup performed in the modules going >> notifier end up acting as a barrier first before freeing the memory ? >> If not, is it explicitly stated that a barrier must be issued before >> module unload ? >> > > You mean rcu_barrier? It is mentioned in the documentation that this is the > responsibility of the module writer to prevent delays for all modules. It's a srcu barrier yes. Considering it would be a barrier specific to the srcu domain within that module, I don't see how it would cause delays for "all" modules if we implicitly issue the barrier on module unload. What am I missing ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com 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=-4.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_PASS autolearn=unavailable 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 88A93C282DD for ; Sun, 7 Apr 2019 20:41:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5358420880 for ; Sun, 7 Apr 2019 20:41:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="bXBuELA+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726477AbfDGUlk (ORCPT ); Sun, 7 Apr 2019 16:41:40 -0400 Received: from mail.efficios.com ([167.114.142.138]:38462 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726397AbfDGUlj (ORCPT ); Sun, 7 Apr 2019 16:41:39 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id B4F4A1D1807; Sun, 7 Apr 2019 16:41:37 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id 1bRHc1aNV_YM; Sun, 7 Apr 2019 16:41:37 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 0ACFC1D1801; Sun, 7 Apr 2019 16:41:37 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 0ACFC1D1801 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1554669697; bh=WBGZowkrGYcSIwNY/4vFGMRq2U8utGqXR14NV18E2io=; h=Date:From:To:Message-ID:MIME-Version; b=bXBuELA+fOPxGTz1EdHkKh4B2jolX6+s6OjUYQgAnSJfhBZDGqyZRH0GtDj88AVxv O4srDRKS89O+wpKO1xvN2/u5h920qvdZeAnzdOky1uQSOvCrPCMjONjO02EZKJOw5v aHV2qIT0c+uQ6UASBBZG+FJ+nuZyxbubPcB/wsYHVdgvV4T+v1f/0e3a/r8BELk4X8 +PdVE7KDn2B8kvvPJbPPOaC+0fEl/MOv+dwDCmnMsQT8jnqkjRZzwOzcc9OjilcpcM w+3r17d0GyylUB3UAukjCBpGrlPW3LMR/20ZFLwN8fGCgdJhArL2gMykR8OpoPZ36r pFh5cDyvinPwQ== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id fEbNe_WclCaN; Sun, 7 Apr 2019 16:41:36 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id DBD551D17FA; Sun, 7 Apr 2019 16:41:36 -0400 (EDT) Date: Sun, 7 Apr 2019 16:41:36 -0400 (EDT) From: Mathieu Desnoyers To: "Joel Fernandes, Google" Cc: paulmck , rcu , linux-kernel , Ingo Molnar , Lai Jiangshan , dipankar , Andrew Morton , Josh Triplett , Thomas Gleixner , Peter Zijlstra , rostedt , David Howells , Eric Dumazet , fweisbec , Oleg Nesterov , linux-nvdimm , dri-devel , amd-gfx Message-ID: <1632568795.549.1554669696728.JavaMail.zimbra@efficios.com> In-Reply-To: <20190407193202.GA30934@localhost> References: <20190402142816.GA13084@linux.ibm.com> <20190403162039.GA14111@linux.ibm.com> <20190405232835.GA24702@linux.ibm.com> <20190406230613.GA187766@google.com> <20190407133941.GC14111@linux.ibm.com> <20190407135937.GA30053@linux.ibm.com> <134026717.535.1554665176677.JavaMail.zimbra@efficios.com> <20190407193202.GA30934@localhost> Subject: Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.12_GA_3794 (ZimbraWebClient - FF66 (Linux)/8.8.12_GA_3794) Thread-Topic: Forbid static SRCU use in modules Thread-Index: ZEmT/F0GhCW2v0mTQFfmYo9Tu0H4dQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Apr 7, 2019, at 3:32 PM, Joel Fernandes, Google joel@joelfernandes.org wrote: > On Sun, Apr 07, 2019 at 03:26:16PM -0400, Mathieu Desnoyers wrote: >> ----- On Apr 7, 2019, at 9:59 AM, paulmck paulmck@linux.ibm.com wrote: >> >> > On Sun, Apr 07, 2019 at 06:39:41AM -0700, Paul E. McKenney wrote: >> >> On Sat, Apr 06, 2019 at 07:06:13PM -0400, Joel Fernandes wrote: >> > >> > [ . . . ] >> > >> >> > > diff --git a/include/asm-generic/vmlinux.lds.h >> >> > > b/include/asm-generic/vmlinux.lds.h >> >> > > index f8f6f04c4453..c2d919a1566e 100644 >> >> > > --- a/include/asm-generic/vmlinux.lds.h >> >> > > +++ b/include/asm-generic/vmlinux.lds.h >> >> > > @@ -338,6 +338,10 @@ >> >> > > KEEP(*(__tracepoints_ptrs)) /* Tracepoints: pointer array */ \ >> >> > > __stop___tracepoints_ptrs = .; \ >> >> > > *(__tracepoints_strings)/* Tracepoints: strings */ \ >> >> > > + . = ALIGN(8); \ >> >> > > + __start___srcu_struct = .; \ >> >> > > + *(___srcu_struct_ptrs) \ >> >> > > + __end___srcu_struct = .; \ >> >> > > } \ >> >> > >> >> > This vmlinux linker modification is not needed. I tested without it and srcu >> >> > torture works fine with rcutorture built as a module. Putting further prints >> >> > in kernel/module.c verified that the kernel is able to find the srcu structs >> >> > just fine. You could squash the below patch into this one or apply it on top >> >> > of the dev branch. >> >> >> >> Good point, given that otherwise FORTRAN named common blocks would not >> >> work. >> >> >> >> But isn't one advantage of leaving that stuff in the RO_DATA_SECTION() >> >> macro that it can be mapped read-only? Or am I suffering from excessive >> >> optimism? >> > >> > And to answer the other question, in the case where I am suffering from >> > excessive optimism, it should be a separate commit. Please see below >> > for the updated original commit thus far. >> > >> > And may I have your Tested-by? >> >> Just to confirm: does the cleanup performed in the modules going >> notifier end up acting as a barrier first before freeing the memory ? >> If not, is it explicitly stated that a barrier must be issued before >> module unload ? >> > > You mean rcu_barrier? It is mentioned in the documentation that this is the > responsibility of the module writer to prevent delays for all modules. It's a srcu barrier yes. Considering it would be a barrier specific to the srcu domain within that module, I don't see how it would cause delays for "all" modules if we implicitly issue the barrier on module unload. What am I missing ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com