From mboxrd@z Thu Jan 1 00:00:00 1970 From: Feng Tang Subject: Re: [PATCH v2] cgroup/cpuset: Remove cpus_allowed/mems_allowed setup in cpuset_init_smp() Date: Tue, 26 Apr 2022 11:23:37 +0800 Message-ID: <20220426032337.GA84190@shbuild999.sh.intel.com> References: <20220425155505.1292896-1-longman@redhat.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1650943421; x=1682479421; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=MIZ9NnOqirQrvhaRVQ8rsuasqFgvVqtc65THhom/L0w=; b=Ca+uNgPHuQDkjgv7MSPDTywLgxBzC/iyQTU2CnojwnDVXz59+n8WeXQD acpcL9Hq0q+tUxYYnlu2X5sBcIOT3lt92a2Xs56Mf0i6IvwIRD3A2euUW ipk0ZJu2KQI0qtHn2qH/5XYI3e7lbCYwvseqcMm3TPdbl0J40Nham8MQ0 k1jQF0gUxzUCXfU284nYDMDOFcLiQdT59xRUoMtcQEC+h2o2z9auIVE9w +qaotL8F7U8cqeMMeh3UtPKO5/mRdJcsxKjXkoTm+R00DElB2gCyoeXEH Jl+vrFUm0Aes9t0Uiz+36vI5k30MMU9Tc5OPFXj2XQd7UQDkr9Mn2HrwX g==; Content-Disposition: inline In-Reply-To: <20220425155505.1292896-1-longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Waiman Long Cc: Tejun Heo , Zefan Li , Johannes Weiner , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Andrew Morton , Michal Hocko , Dave Hansen , ying.huang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org 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. > 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.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]; ? Thanks, Feng