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 A055FC4360F for ; Wed, 3 Apr 2019 16:20:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 602FF206C0 for ; Wed, 3 Apr 2019 16:20:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726574AbfDCQUu (ORCPT ); Wed, 3 Apr 2019 12:20:50 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:37472 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725990AbfDCQUt (ORCPT ); Wed, 3 Apr 2019 12:20:49 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x33GF9NA007822 for ; Wed, 3 Apr 2019 12:20:48 -0400 Received: from e13.ny.us.ibm.com (e13.ny.us.ibm.com [129.33.205.203]) by mx0b-001b2d01.pphosted.com with ESMTP id 2rmxqvw9f7-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 03 Apr 2019 12:20:47 -0400 Received: from localhost by e13.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 3 Apr 2019 17:20:46 +0100 Received: from b01cxnp22033.gho.pok.ibm.com (9.57.198.23) by e13.ny.us.ibm.com (146.89.104.200) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 3 Apr 2019 17:20:41 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x33GKeN422020310 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 3 Apr 2019 16:20:40 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3FF20B2065; Wed, 3 Apr 2019 16:20:40 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E00B5B205F; Wed, 3 Apr 2019 16:20:39 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.80.202.55]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 3 Apr 2019 16:20:39 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id C026816C2664; Wed, 3 Apr 2019 09:20:39 -0700 (PDT) Date: Wed, 3 Apr 2019 09:20:39 -0700 From: "Paul E. McKenney" To: Mathieu Desnoyers Cc: rcu , linux-kernel , Ingo Molnar , Lai Jiangshan , dipankar , Andrew Morton , Josh Triplett , Thomas Gleixner , Peter Zijlstra , rostedt , David Howells , Eric Dumazet , fweisbec , Oleg Nesterov , "Joel Fernandes, Google" , linux-nvdimm , dri-devel , amd-gfx Subject: Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules Reply-To: paulmck@linux.ibm.com References: <20190402142816.GA13084@linux.ibm.com> <886051277.1395.1554218080591.JavaMail.zimbra@efficios.com> <20190402152334.GC4102@linux.ibm.com> <161156422.1435.1554219247444.JavaMail.zimbra@efficios.com> <20190403133243.GE4102@linux.ibm.com> <1028306587.504.1554301662374.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1028306587.504.1554301662374.JavaMail.zimbra@efficios.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19040316-0064-0000-0000-000003C5F4CA X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010867; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000284; SDB=6.01183798; UDB=6.00619788; IPR=6.00964550; MB=3.00026279; MTD=3.00000008; XFM=3.00000015; UTC=2019-04-03 16:20:46 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19040316-0065-0000-0000-00003CEFB2BB Message-Id: <20190403162039.GA14111@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-03_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904030110 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 03, 2019 at 10:27:42AM -0400, Mathieu Desnoyers wrote: > ----- On Apr 3, 2019, at 9:32 AM, paulmck paulmck@linux.ibm.com wrote: > > > On Tue, Apr 02, 2019 at 11:34:07AM -0400, Mathieu Desnoyers wrote: > >> ----- On Apr 2, 2019, at 11:23 AM, paulmck paulmck@linux.ibm.com wrote: > >> > >> > On Tue, Apr 02, 2019 at 11:14:40AM -0400, Mathieu Desnoyers wrote: > >> >> ----- On Apr 2, 2019, at 10:28 AM, paulmck paulmck@linux.ibm.com wrote: > >> >> > >> >> > Hello! > >> >> > > >> >> > This series prohibits use of DEFINE_SRCU() and DEFINE_STATIC_SRCU() > >> >> > by loadable modules. The reason for this prohibition is the fact > >> >> > that using these two macros within modules requires that the size of > >> >> > the reserved region be increased, which is not something we want to > >> >> > be doing all that often. Instead, loadable modules should define an > >> >> > srcu_struct and invoke init_srcu_struct() from their module_init function > >> >> > and cleanup_srcu_struct() from their module_exit function. Note that > >> >> > modules using call_srcu() will also need to invoke srcu_barrier() from > >> >> > their module_exit function. > >> >> > >> >> This arbitrary API limitation seems weird. > >> >> > >> >> Isn't there a way to allow modules to use DEFINE_SRCU and DEFINE_STATIC_SRCU > >> >> while implementing them with dynamic allocation under the hood ? > >> > > >> > Although call_srcu() already has initialization hooks, some would > >> > also be required in srcu_read_lock(), and I am concerned about adding > >> > memory allocation at that point, especially given the possibility > >> > of memory-allocation failure. And the possibility that the first > >> > srcu_read_lock() happens in an interrupt handler or similar. > >> > > >> > Or am I missing a trick here? > >> > >> I was more thinking that under #ifdef MODULE, both DEFINE_SRCU and > >> DEFINE_STATIC_SRCU could append data in a dedicated section. module.c > >> would additionally lookup that section on module load, and deal with > >> those statically defined SRCU entries as if they were dynamically > >> allocated ones. It would of course cleanup those resources on module > >> unload. > >> > >> Am I missing some subtlety there ? > > > > If I understand you correctly, that is actually what is already done. The > > size of this dedicated section is currently set by PERCPU_MODULE_RESERVE, > > and the additions of DEFINE{_STATIC}_SRCU() in modules was requiring that > > this to be increased frequently. That led to a request that something > > be done, in turn leading to this patch series. > > I think we are not expressing quite the same idea. > > AFAIU, yours is to have DEFINE*_SRCU directly define per-cpu data within modules, > which ends up using percpu module reserved memory. > > My idea is to make DEFINE*_SRCU have a different behavior under #ifdef MODULE. > It could emit a _global variable_ (_not_ per-cpu) within a new section. That > section would then be used by module init/exit code to figure out what "srcu > descriptors" are present in the modules. It would therefore rely on dynamic > allocation for those, therefore removing the need to involve the percpu module > reserved pool at all. > > > > > I don't see a way around this short of changing module loading to do > > alloc_percpu() and then updating the relocation based on this result. > > Which would admittedly be far more convenient. I was assuming that > > this would be difficult due to varying CPU offsets or the like. > > > > But if it can be done reasonably, it would be quite a bit nicer than > > forcing dynamic allocation in cases where it is not otherwise needed. > > Hopefully my explanation above helps clear out what I have in mind. > > You can find similar tricks performed by include/linux/tracepoint.h: > > #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS > static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > { > return offset_to_ptr(p); > } > > #define __TRACEPOINT_ENTRY(name) \ > asm(" .section \"__tracepoints_ptrs\", \"a\" \n" \ > " .balign 4 \n" \ > " .long __tracepoint_" #name " - . \n" \ > " .previous \n") > #else > static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > { > return *p; > } > > #define __TRACEPOINT_ENTRY(name) \ > static tracepoint_ptr_t __tracepoint_ptr_##name __used \ > __attribute__((section("__tracepoints_ptrs"))) = \ > &__tracepoint_##name > #endif > > [...] > > #define DEFINE_TRACE_FN(name, reg, unreg) \ > static const char __tpstrtab_##name[] \ > __attribute__((section("__tracepoints_strings"))) = #name; \ > struct tracepoint __tracepoint_##name \ > __attribute__((section("__tracepoints"), used)) = \ > { __tpstrtab_##name, STATIC_KEY_INIT_FALSE, reg, unreg, NULL };\ > __TRACEPOINT_ENTRY(name); > > And kernel/module.c: > > find_module_sections(): > > #ifdef CONFIG_TRACEPOINTS > mod->tracepoints_ptrs = section_objs(info, "__tracepoints_ptrs", > sizeof(*mod->tracepoints_ptrs), > &mod->num_tracepoints); > #endif > > And kernel/tracepoint.c:tracepoint_module_notify() for the module coming/going > notifier. > > Basically you would want to have your own structure within your own section of > the module which describes the srcu domain, and have a module coming/going > notifier responsible for dynamically allocating the srcu domain on "coming", and > doing a srcu barrier and cleanup the domain on "going". Ah, sounds like an excellent approach! I will give it a shot, thank you! Thanx, Paul > Thanks, > > Mathieu > > > > > > Thanx, Paul > > > >> Thanks, > >> > >> Mathieu > >> > >> > >> > > >> > Thanx, Paul > >> > > >> >> Thanks, > >> >> > >> >> Mathieu > >> >> > >> >> > >> >> > > >> >> > This series consist of the following: > >> >> > > >> >> > 1. Dynamically allocate dax_srcu. > >> >> > > >> >> > 2. Dynamically allocate drm_unplug_srcu. > >> >> > > >> >> > 3. Dynamically allocate kfd_processes_srcu. > >> >> > > >> >> > These build and have been subjected to 0day testing, but might also need > >> >> > testing by someone having the requisite hardware. > >> >> > > >> >> > Thanx, Paul > >> >> > > >> >> > ------------------------------------------------------------------------ > >> >> > > >> >> > drivers/dax/super.c | 10 +++++- > >> >> > drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c | 5 +++ > >> >> > drivers/gpu/drm/amd/amdkfd/kfd_process.c | 2 - > >> >> > drivers/gpu/drm/drm_drv.c | 8 ++++ > >> >> > include/linux/srcutree.h | 19 +++++++++-- > >> >> > kernel/rcu/rcuperf.c | 40 +++++++++++++++++++----- > >> >> > kernel/rcu/rcutorture.c | 48 +++++++++++++++++++++-------- > >> >> > 7 files changed, 105 insertions(+), 27 deletions(-) > >> >> > >> >> -- > >> >> Mathieu Desnoyers > >> >> EfficiOS Inc. > >> >> http://www.efficios.com > >> > >> -- > >> Mathieu Desnoyers > >> EfficiOS Inc. > >> http://www.efficios.com > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com >