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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4BA3FC433F5 for ; Wed, 27 Apr 2022 01:07:02 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5EB8E6B0073; Tue, 26 Apr 2022 21:07:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 572E66B0075; Tue, 26 Apr 2022 21:07:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3EBB66B0078; Tue, 26 Apr 2022 21:07:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.a.hostedemail.com [64.99.140.24]) by kanga.kvack.org (Postfix) with ESMTP id 29D986B0073 for ; Tue, 26 Apr 2022 21:07:01 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id E9B0927E20 for ; Wed, 27 Apr 2022 01:07:00 +0000 (UTC) X-FDA: 79400869800.16.B9FEB13 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by imf12.hostedemail.com (Postfix) with ESMTP id 58C0540046 for ; Wed, 27 Apr 2022 01:06:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1651021620; x=1682557620; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=qXiurggk6lNRwvUejqTYj42K/KnKmAqkVluTK7PeL+g=; b=VNct4w0oO7vYLxk0kQW3VFYFvCyPx9/wkLQCbRJeeXJk1UGGq4lhGZBP ZKPwL2TirljZZJYYKCHVBWXmBBWvIUZNgxCVCehUFAbAULHMirp4BzYtB TiZa+woVV4rNv7OzGf50cn0RNGQHjaaHnQedmsoeOu8HUrN5eqZ0JTBaw KVO0AvLzTp9FTnR7C9Fy2ThF8+5SZvTPYBfXOmLg5wz3k6O9jUimHbqxB Z2XBpGAcjckPeurkVuY6ERAoZZcEy2FsR3Pl+Lix2y1wlSdV1D1ZLn+cK SHA9m6PUoWRUaezhOb12rt8Tp4tnOYwtjlQ9uNNwG/CBmPqggXBWkzTV0 g==; X-IronPort-AV: E=McAfee;i="6400,9594,10329"; a="264620040" X-IronPort-AV: E=Sophos;i="5.90,292,1643702400"; d="scan'208";a="264620040" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Apr 2022 18:06:58 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.90,292,1643702400"; d="scan'208";a="558635915" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.146.138]) by orsmga007.jf.intel.com with ESMTP; 26 Apr 2022 18:06:55 -0700 Date: Wed, 27 Apr 2022 09:06:54 +0800 From: Feng Tang To: Waiman Long Cc: Tejun Heo , Zefan Li , Johannes Weiner , "cgroups@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Michal Hocko , "Hansen, Dave" , "Huang, Ying" , "stable@vger.kernel.org" Subject: Re: [PATCH v2] cgroup/cpuset: Remove cpus_allowed/mems_allowed setup in cpuset_init_smp() Message-ID: <20220427010654.GC84190@shbuild999.sh.intel.com> References: <20220425155505.1292896-1-longman@redhat.com> <20220426032337.GA84190@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 58C0540046 X-Stat-Signature: zadannyerw6wm75kc1qd55irmthdujft X-Rspam-User: Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=VNct4w0o; spf=none (imf12.hostedemail.com: domain of feng.tang@intel.com has no SPF policy when checking 192.55.52.120) smtp.mailfrom=feng.tang@intel.com; dmarc=pass (policy=none) header.from=intel.com X-Rspamd-Server: rspam09 X-HE-Tag: 1651021611-697208 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 26, 2022 at 10:58:21PM +0800, Waiman Long wrote: > On 4/25/22 23:23, Feng Tang wrote: > > Hi Waiman, > > > > On Mon, Apr 25, 2022 at 11:55:05AM -0400, Waiman Long wrote: > >> There are 3 places where the cpu and node masks of the top cpuset can > >> be initialized in the order they are executed: > >> 1) start_kernel -> cpuset_init() > >> 2) start_kernel -> cgroup_init() -> cpuset_bind() > >> 3) kernel_init_freeable() -> do_basic_setup() -> cpuset_init_smp() > >> > >> The first cpuset_init() function just sets all the bits in the masks. > >> The last one executed is cpuset_init_smp() which sets up cpu and node > >> masks suitable for v1, but not v2. cpuset_bind() does the right setup > >> for both v1 and v2. > >> > >> For systems with cgroup v2 setup, cpuset_bind() is called once. For > >> systems with cgroup v1 setup, cpuset_bind() is called twice. It is > >> first called before cpuset_init_smp() in cgroup v2 mode. Then it is > >> called again when cgroup v1 filesystem is mounted in v1 mode after > >> cpuset_init_smp(). > >> > >> [ 2.609781] cpuset_bind() called - v2 = 1 > >> [ 3.079473] cpuset_init_smp() called > >> [ 7.103710] cpuset_bind() called - v2 = 0 > > I run some test, on a server with centOS, this did happen that > > cpuset_bind() is called twice, first as v2 during kernel boot, > > and then as v1 post-boot. > > > > However on a QEMU running with a basic debian rootfs image, > > the second call of cpuset_bind() didn't happen. > > The first time cpuset_bind() is called in cgroup_init(), the kernel > doesn't know if userspace is going to mount v1 or v2 cgroup. By default, > it is assumed to be v2. However, if userspace mounts the cgroup v1 > filesystem for cpuset, cpuset_bind() will be run at this point by > rebind_subsystem() to set up cgroup v1 environment and > cpus_allowed/mems_allowed will be correctly set at this point. Mounting > the cgroup v2 filesystem, however, does not cause rebind_subsystem() to > run and hence cpuset_bind() is not called again. > > Is the QEMU setup not mounting any cgroup filesystem at all? If so, does > it matter whether v1 or v2 setup is used? When I got the cpuset binding error report, I tried first on qemu to reproduce and failed (due to there was no memory hotplug), then I reproduced it on a real server. For both system, I used "cgroup_no_v1=all" cmdline parameter to test cgroup-v2, could this be the reason? (TBH, this is the first time I use cgroup-v2). Here is the info dump: # mount | grep cgroup tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755) cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd) #cat /proc/filesystems | grep cgroup nodev cgroup nodev cgroup2 Thanks, Feng > >> As a result, cpu and memory node hot add may fail to update the cpu and > >> node masks of the top cpuset to include the newly added cpu or node in > >> a cgroup v2 environment. > >> > >> smp_init() is called after the first two init functions. So we don't > >> have a complete list of active cpus and memory nodes until later in > >> cpuset_init_smp() which is the right time to set up effective_cpus > >> and effective_mems. > >> > >> To fix this problem, the potentially incorrect cpus_allowed & > >> mems_allowed setup in cpuset_init_smp() are removed. For cgroup v2 > >> systems, the initial cpuset_bind() call will set them up correctly. > >> For cgroup v1 systems, the second call to cpuset_bind() will do the > >> right setup. > >> > >> cc: stable@vger.kernel.org > >> Signed-off-by: Waiman Long > >> --- > >> kernel/cgroup/cpuset.c | 5 +++-- > >> 1 file changed, 3 insertions(+), 2 deletions(-) > >> > >> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > >> index 9390bfd9f1cd..6bd8f5ef40fe 100644 > >> --- a/kernel/cgroup/cpuset.c > >> +++ b/kernel/cgroup/cpuset.c > >> @@ -3390,8 +3390,9 @@ static struct notifier_block cpuset_track_online_nodes_nb = { > >> */ > >> void __init cpuset_init_smp(void) > >> { > >> - cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask); > >> - top_cpuset.mems_allowed = node_states[N_MEMORY]; > > So can we keep line > > cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask); > > > > and only remove line > > top_cpuset.mems_allowed = node_states[N_MEMORY]; > > ? > > That may cause cpusets.cpu to be set incorrectly for systems using > cgroup v2. What is really important is that effective_cpus and > effective_mems are set correctly. > > Cheers, > Longman >