Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756330AbdLOTGl (ORCPT ); Fri, 15 Dec 2017 14:06:41 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:43014 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756221AbdLOTGi (ORCPT ); Fri, 15 Dec 2017 14:06:38 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org C46CA60B17 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=prsood@codeaurora.org Subject: Re: [PATCH] cgroup/cpuset: fix circular locking dependency To: Tejun Heo Cc: Peter Zijlstra , avagin@gmail.com, mingo@kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, sramana@codeaurora.org References: <623f214b-8b9a-f967-7a3d-ca9c06151267@codeaurora.org> <20171204202219.GF2421075@devbig577.frc2.facebook.com> <20171204225825.GP2421075@devbig577.frc2.facebook.com> <20171204230117.GF20227@worktop.programming.kicks-ass.net> <4e63b5e9-1696-910f-16ac-4d4d7eb98725@codeaurora.org> <40968aea-cd73-5ce4-d559-962d91e315c5@codeaurora.org> <20171211153258.GI2421075@devbig577.frc2.facebook.com> <20171213154041.GP3919388@devbig577.frc2.facebook.com> <20171215132222.GF3919388@devbig577.frc2.facebook.com> From: Prateek Sood Message-ID: Date: Sat, 16 Dec 2017 00:36:33 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20171215132222.GF3919388@devbig577.frc2.facebook.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1364 Lines: 39 On 12/15/2017 06:52 PM, Tejun Heo wrote: > Hello, Prateek. > > On Fri, Dec 15, 2017 at 02:24:55PM +0530, Prateek Sood wrote: >> Following are two ways to improve cgroup_transfer_tasks(). In >> both cases task in PF_EXITING state would be left in source >> cgroup. It would be removed from cgroup_exit() in exit path. >> >> diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c >> index 024085d..e2bdcdb 100644 >> --- a/kernel/cgroup/cgroup-v1.c >> +++ b/kernel/cgroup/cgroup-v1.c >> @@ -123,7 +123,10 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from) >> */ >> do { >> css_task_iter_start(&from->self, 0, &it); >> - task = css_task_iter_next(&it); >> + do { >> + task = css_task_iter_next(&it); >> + } while (task && (task & PF_EXITING)) >> + > > Yeah, this looks good to me. We can't just make a single pass as in > the other one because we can race aginst fork. And PF_EXITING being > left behind is what was happening previously too anyway. They can't > be moved. > > Thanks. > Thanks TJ for reviewing. I will send a formal patch with the above approved approach. -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project