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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_SANE_1 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 92509C32750 for ; Fri, 2 Aug 2019 06:20:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 662B6206A3 for ; Fri, 2 Aug 2019 06:20:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731663AbfHBGUz (ORCPT ); Fri, 2 Aug 2019 02:20:55 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:32997 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729316AbfHBGUy (ORCPT ); Fri, 2 Aug 2019 02:20:54 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R771e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04391;MF=kerneljasonxing@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0TYSHu-K_1564726826; Received: from ali-6c96cfdd2b5d.local(mailfrom:kerneljasonxing@linux.alibaba.com fp:SMTPD_---0TYSHu-K_1564726826) by smtp.aliyun-inc.com(127.0.0.1); Fri, 02 Aug 2019 14:20:52 +0800 Subject: Re: [PATCH v2] psi: get poll_work to run when calling poll syscall next time To: hannes@cmpxchg.org, surenb@google.com Cc: dennis@kernel.org, mingo@redhat.com, axboe@kernel.dk, lizefan@huawei.com, peterz@infradead.org, tj@kernel.org, linux-kernel@vger.kernel.org, caspar@linux.alibaba.com, joseph.qi@linux.alibaba.com References: <1563864339-2621-1-git-send-email-kerneljasonxing@linux.alibaba.com> <1564463819-120014-1-git-send-email-kerneljasonxing@linux.alibaba.com> From: Jason Xing Message-ID: <63ac943a-dc9a-f987-3580-6a0d3192e1dd@linux.alibaba.com> Date: Fri, 2 Aug 2019 14:20:26 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <1564463819-120014-1-git-send-email-kerneljasonxing@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, According to the reviews from Johoannes, I've changed the old patch and then submitted the version 2 patch a few days ago. Please let me know if all this sounds good, or if there are any issues. Thanks, Jason On 2019/7/30 下午1:16, Jason Xing wrote: > Only when calling the poll syscall the first time can user > receive POLLPRI correctly. After that, user always fails to > acquire the event signal. > > Reproduce case: > 1. Get the monitor code in Documentation/accounting/psi.txt > 2. Run it, and wait for the event triggered. > 3. Kill and restart the process. > > If the user doesn't kill the monitor process, it seems the > poll_work works fine. After killing and restarting the monitor, > the poll_work in kernel will never run again due to the wrong > value of poll_scheduled. Therefore, we should reset the value > as group_init() does after the last trigger is destroyed. > > [PATCH V2] > In the patch v2, I put the atomic_set(&group->poll_scheduled, 0); > into the right place. > Here I quoted from Johannes as the best explaination: > "The question is why we can end up with poll_scheduled = 1 but the work > not running (which would reset it to 0). And the answer is because the > scheduling side sees group->poll_kworker under RCU protection and then > schedules it, but here we cancel the work and destroy the worker. The > cancel needs to pair with resetting the poll_scheduled flag." > > Signed-off-by: Jason Xing > Reviewed-by: Caspar Zhang > Reviewed-by: Joseph Qi > Reviewed-by: Suren Baghdasaryan > Acked-by: Johannes Weiner > --- > kernel/sched/psi.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > index 7acc632..acdada0 100644 > --- a/kernel/sched/psi.c > +++ b/kernel/sched/psi.c > @@ -1131,7 +1131,14 @@ static void psi_trigger_destroy(struct kref *ref) > * deadlock while waiting for psi_poll_work to acquire trigger_lock > */ > if (kworker_to_destroy) { > + /* > + * After the RCU grace period has expired, the worker > + * can no longer be found through group->poll_kworker. > + * But it might have been already scheduled before > + * that - deschedule it cleanly before destroying it. > + */ > kthread_cancel_delayed_work_sync(&group->poll_work); > + atomic_set(&group->poll_scheduled, 0); > kthread_destroy_worker(kworker_to_destroy); > } > kfree(t); >