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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 A972AC169C4 for ; Thu, 31 Jan 2019 14:56:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7497D218F0 for ; Thu, 31 Jan 2019 14:56:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548946586; bh=bzMTTgRyGCbRDBHIrbsuD4dgSoDd5YrD4DzXeA71LWU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=oA83GWiht9S/0UKY74z/j2DThZkP4Q/bGxiEuk2uldO43cjBTlSMwxajIVYSIughQ HV7U0wWzedyTNDCWEhNDOVI3BZxWWeKqkx5TNvyc4UFacbnThfPXY2SrABi5MtilJz EeMi1VrcPjLI1nfG1d0iiApTgd9cKlIfauuL07XY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732474AbfAaO4Y (ORCPT ); Thu, 31 Jan 2019 09:56:24 -0500 Received: from mail-yb1-f193.google.com ([209.85.219.193]:45931 "EHLO mail-yb1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725796AbfAaO4Y (ORCPT ); Thu, 31 Jan 2019 09:56:24 -0500 Received: by mail-yb1-f193.google.com with SMTP id t11so1375897ybi.12; Thu, 31 Jan 2019 06:56:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=wqkae5/SZUXV0XpHwrdhyDmdmZuXObNbFvC+52gNI10=; b=T+tfKU9bLG/Ze8iEPeVXdRWijWD8iEUGg5hxZ7uE66Rm49Duni5enxE3uJgCj0ClBE 8OHx1m0Y2s0wwyJHaSsN76bNKEbEG0RWW2e/Ft212//gGXoVP+sO1/qflAXTBx+FwUiS icEdvmjlo+NbU2KspZtxwijuTJEK40AKekvdtptVupBJ5hN23RQdGH9bPORrBFsiB59S eA+FsM2mQKfMnbjlR3cIWbUHKOfV0+fGr8LQPdnG3qcRwTzAK8lcHMa37eXx9CWGuAn5 MvTn09SulsASG7+Bii1yDxsMlik+rv0QvEZYmbMwOyPxR9gviKae5xbVAcFtBvh+Xo0c 1HiA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=wqkae5/SZUXV0XpHwrdhyDmdmZuXObNbFvC+52gNI10=; b=jClTGT5A/4PZLru3cFAGzfC51/g/84da9f9agQXCk5uqbaYEAnj/GBIFJ6I9tNykB5 K+D298pqATYxW/cJUITSEPh042bDD6bzN/ktkxqb6CJ1DhFctYW5zA94m/KLCUZBBm02 /7eV+rN2fXTvrb7iOamrPx3GE01YMKnXDJ9xUrlyD6DjCwMyT4B+GyBefbI758WlRNJ4 dmxRRlR8ggX91PhdWs+m41amZTBmZh1oVXZvXwWhiCJuOwpgSKXyNlPp2pqPFf+q/B3i rrNhnjvO9+8RCaRM7Yc/Vaaa2HuS5LSVmGLp0j3MOZt2gw0DccyQijvKfT/YKDS8EH2g i+2A== X-Gm-Message-State: AHQUAubgTzFlHoGd9QZfHjLykTtZ1Nq6sSe3f0Mqr/a1mZylhgbQw68C TXlFZZvj8AYpyBA69gB9sq4= X-Google-Smtp-Source: AHgI3IbN//PVesytuT4ildCDrP3BYEXd6batBNJ0s56TIfUQfrflfE1eViTQwdfJVS6+wmyfKc03VA== X-Received: by 2002:a25:3503:: with SMTP id c3mr6148458yba.321.1548946582781; Thu, 31 Jan 2019 06:56:22 -0800 (PST) Received: from localhost ([2620:10d:c091:200::5:b53a]) by smtp.gmail.com with ESMTPSA id r188sm1666201ywb.30.2019.01.31.06.56.21 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Jan 2019 06:56:21 -0800 (PST) Date: Thu, 31 Jan 2019 06:56:20 -0800 From: Tejun Heo To: Oleg Nesterov Cc: Johannes Weiner , Li Zefan , Herton Krzesinski , Jan Stancek , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] cgroup/pids: turn cgroup_subsys->free() into cgroup_subsys->release() to fix the accounting Message-ID: <20190131145620.GC50184@devbig004.ftw2.facebook.com> References: <20190128160013.GA21219@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190128160013.GA21219@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 28, 2019 at 05:00:13PM +0100, Oleg Nesterov wrote: > The only user of cgroup_subsys->free() callback is pids_cgrp_subsys which > needs pids_free() to uncharge the pid. > > However, ->free() is called from __put_task_struct()->cgroup_free() and this > is too late. Even the trivial program which does > > for (;;) { > int pid = fork(); > assert(pid >= 0); > if (pid) > wait(NULL); > else > exit(0); > } > > can run out of limits because release_task()->call_rcu(delayed_put_task_struct) > implies an RCU gp after the task/pid goes away and before the final put(). > > Test-case: > > mkdir -p /tmp/CG > mount -t cgroup2 none /tmp/CG > echo '+pids' > /tmp/CG/cgroup.subtree_control > > mkdir /tmp/CG/PID > echo 2 > /tmp/CG/PID/pids.max > > perl -e 'while ($p = fork) { wait; } $p // die "fork failed: $!\n"' & > echo $! > /tmp/CG/PID/cgroup.procs > > Without this patch the forking process fails soon after migration. > > Rename cgroup_subsys->free() to cgroup_subsys->release() and move the callsite > into the new helper, cgroup_release(), called by release_task() which actually > frees the pid(s). > > Reported-by: Herton R. Krzesinski > Reported-by: Jan Stancek > Signed-off-by: Oleg Nesterov Applied to cgroup/for-5.0. Thanks, Oleg. -- tejun