FAILED: patch "[PATCH] cgroup/cpuset: Fix a race between cpuset_attach() and cpu" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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 <[email protected]>.

thanks,

greg k-h

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

From 05c7b7a92cc87ff8d7fde189d0fade250697573c Mon Sep 17 00:00:00 2001
From: Zhang Qiao <[email protected]>
Date: Fri, 21 Jan 2022 18:12:10 +0800
Subject: [PATCH] cgroup/cpuset: Fix a race between cpuset_attach() and cpu
hotplug
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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.

index 4c7254e8f49a..97c53f3cc917 100644
@@ -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 */