From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934311AbcLMTMu (ORCPT ); Tue, 13 Dec 2016 14:12:50 -0500 Received: from mail-db5eur01on0096.outbound.protection.outlook.com ([104.47.2.96]:60779 "EHLO EUR01-DB5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752826AbcLMTMs (ORCPT ); Tue, 13 Dec 2016 14:12:48 -0500 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=aryabinin@virtuozzo.com; Subject: Re: [PATCH] mm-add-vfree_atomic-fix To: Michal Hocko , Andy Lutomirski References: <87lgvlzp34.fsf@yhuang-dev.intel.com> <1481553981-3856-1-git-send-email-aryabinin@virtuozzo.com> <20161213101254.GC10498@dhcp22.suse.cz> <20161213172441.GA22610@dhcp22.suse.cz> CC: Andrew Morton , Huang Ying , Stephen Rothwell , Christoph Hellwig , Joel Fernandes , Jisheng Zhang , Chris Wilson , John Dias , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , "linux-kernel@vger.kernel.org" , LKP From: Andrey Ryabinin Message-ID: Date: Tue, 13 Dec 2016 22:06:14 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <20161213172441.GA22610@dhcp22.suse.cz> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [84.47.128.244] X-ClientProxiedBy: HE1PR0101CA0013.eurprd01.prod.exchangelabs.com (10.168.141.151) To DB6PR0801MB2053.eurprd08.prod.outlook.com (10.168.86.22) X-MS-Office365-Filtering-Correlation-Id: 2c517abd-85a8-4245-c5b6-08d4238c04e8 X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001);SRVR:DB6PR0801MB2053; X-Microsoft-Exchange-Diagnostics: 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12/13/2016 08:24 PM, Michal Hocko wrote: > On Tue 13-12-16 08:57:34, Andy Lutomirski wrote: >> On Tue, Dec 13, 2016 at 2:12 AM, Michal Hocko wrote: >>> [CC Andy] >>> >>> I've noticed the same >>> http://lkml.kernel.org/r/20161209142820.GA4334@dhcp22.suse.cz >>> and also concluded same as you >>> >>> On Mon 12-12-16 17:46:21, Andrey Ryabinin wrote: >>>> DEBUG_PREEMPT complains about using this_cpu_ptr() in preemptible: >>>> BUG: using smp_processor_id() in preemptible [00000000] code: iperf-300s-cs-l/277 >>>> caller is debug_smp_processor_id+0x17/0x19 >>>> CPU: 1 PID: 277 Comm: iperf-300s-cs-l Not tainted 4.9.0-rc8-00140-gcc639db #2 >>>> ffffc900003f3cf0 ffffffff8123ae6f 0000000000000001 ffffffff818181da >>>> ffffc900003f3d20 ffffffff81252f41 0000000000012de0 00000000fffffdff >>>> ffff880009328f40 ffff88000592c400 ffffc900003f3d30 ffffffff81252f6a >>>> Call Trace: >>>> [] dump_stack+0x9a/0xd0 >>>> [] check_preemption_disabled+0xdd/0xef >>>> [] debug_smp_processor_id+0x17/0x19 >>>> [] __vfree_deferred+0x16/0x4c >>>> [] vfree_atomic+0x22/0x24 >>>> [] free_thread_stack+0xc2/0x106 >>>> [] put_task_stack+0x4c/0x62 >>>> [] copy_process+0x7e0/0x16e8 >>>> [] _do_fork+0xbb/0x2d3 >>>> [] ? __do_page_fault+0x2e1/0x384 >>>> [] ? trace_hardirqs_off_caller+0x12/0x24 >>>> [] SyS_clone+0x19/0x1b >>>> [] do_syscall_64+0x143/0x173 >>>> [] entry_SYSCALL64_slow_path+0x25/0x25 >>>> >>>> Use raw_cpu_ptr() instead of this_cpu_ptr() to hide this warning. >>>> It's fine because llist_add() implementation is lock-less, so it works even >>>> if we adding to the list of some other cpu. schedule_work() is also preempt-safe. >>>> >>>> Reported-by: kernel test robot >>>> Signed-off-by: Andrey Ryabinin >>> >>> Acked-by: Michal Hocko >> >> But not quite acked by me. What happened to the vfree code that >> causes vfree_deferred to be called in a preemptable context? That >> sounds like a bug. > > Not sure I understand but the above stack points to a preemptible > context (copy_process). My stack was different and it looks preemptible as well. > free_thread_stack calls vfree_atomic unconditionally. So I am not sure > why do you think this is a bug? > >> (This code doesn't exist in Linus' tree. What tree does this apply to.) > > Anyway, now that I am looking at Andrew's tree I can see [1] which > doesn't have this_cpu_ptr. So I am not sure where this this_cpu_ptr came > from. Maybe the previous version of the patch which has shown up in the > linux-next and Andrew has picked up [2] in the meantime. /me confused > this_cpu_ptr() comes from the original patch http://lkml.kernel.org/r/1479474236-4139-5-git-send-email-hch@lst.de Andrew picked up [2] and folded-merged it into original patch and sent it to Linus. Now it in Linus tree, commit bf22e37a641327e34681b7b6959d9646e3886 > [1] http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-add-vfree_atomic.patch > [2] http://lkml.kernel.org/r/1481553981-3856-1-git-send-email-aryabinin@virtuozzo.com >