The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 05c7b7a92cc87ff8d7fde189d0fade250697573c Mon Sep 17 00:00:00 2001 From: Zhang Qiao zhangqiao22@huawei.com Date: Fri, 21 Jan 2022 18:12:10 +0800 Subject: [PATCH] cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

As previously discussed(https://lkml.org/lkml/2022/1/20/51), cpuset_attach() is affected with similar cpu hotplug race, as follow scenario:

cpuset_attach() cpu hotplug --------------------------- ---------------------- down_write(cpuset_rwsem) guarantee_online_cpus() // (load cpus_attach) sched_cpu_deactivate set_cpu_active() // will change cpu_active_mask set_cpus_allowed_ptr(cpus_attach) __set_cpus_allowed_ptr_locked() // (if the intersection of cpus_attach and cpu_active_mask is empty, will return -EINVAL) up_write(cpuset_rwsem)

To avoid races such as described above, protect cpuset_attach() call with cpu_hotplug_lock.

Fixes: be367d099270 ("cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time") Cc: stable@vger.kernel.org # v2.6.32+ Reported-by: Zhao Gongyi zhaogongyi@huawei.com Signed-off-by: Zhang Qiao zhangqiao22@huawei.com Acked-by: Waiman Long longman@redhat.com Reviewed-by: Michal Koutný mkoutny@suse.com Signed-off-by: Tejun Heo tj@kernel.org

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 4c7254e8f49a..97c53f3cc917 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2289,6 +2289,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) cgroup_taskset_first(tset, &css); cs = css_cs(css);

+ cpus_read_lock(); percpu_down_write(&cpuset_rwsem);

guarantee_online_mems(cs, &cpuset_attach_nodemask_to); @@ -2342,6 +2343,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) wake_up(&cpuset_attach_wq);

percpu_up_write(&cpuset_rwsem); + cpus_read_unlock(); }

/* The various types of files and directories in a cpuset file system */