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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Zhao Gongyi <zhaogongyi@huawei.com>,
        Zhang Qiao <zhangqiao22@huawei.com>,
        Waiman Long <longman@redhat.com>,
        =?UTF-8?q?Michal=20Koutn=C3=BD?= <mkoutny@suse.com>,
        Tejun Heo <tj@kernel.org>
Subject: [PATCH 4.19 01/34] cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug
Date:   Mon, 28 Feb 2022 18:24:07 +0100
Message-Id: <20220228172208.566431934@linuxfoundation.org>
In-Reply-To: <20220228172207.090703467@linuxfoundation.org>
References: <20220228172207.090703467@linuxfoundation.org>
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From: Zhang Qiao <zhangqiao22@huawei.com>

commit 05c7b7a92cc87ff8d7fde189d0fade250697573c upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/cgroup/cpuset.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1528,6 +1528,7 @@ static void cpuset_attach(struct cgroup_
 	cgroup_taskset_first(tset, &css);
 	cs = css_cs(css);
 
+	cpus_read_lock();
 	mutex_lock(&cpuset_mutex);
 
 	/* prepare for attach */
@@ -1583,6 +1584,7 @@ static void cpuset_attach(struct cgroup_
 		wake_up(&cpuset_attach_wq);
 
 	mutex_unlock(&cpuset_mutex);
+	cpus_read_unlock();
 }
 
 /* The various types of files and directories in a cpuset file system */