Merge branch 'for-5.7' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:

 - Christian extended clone3 so that processes can be spawned into
   cgroups directly.

   This is not only neat in terms of semantics but also avoids grabbing
   the global cgroup_threadgroup_rwsem for migration.

 - Daniel added !root xattr support to cgroupfs.

   Userland already uses xattrs on cgroupfs for bookkeeping. This will
   allow delegated cgroups to support such usages.

 - Prateek tried to make cpuset hotplug handling synchronous but that
   led to possible deadlock scenarios. Reverted.

 - Other minor changes including release_agent_path handling cleanup.

* 'for-5.7' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  docs: cgroup-v1: Document the cpuset_v2_mode mount option
  Revert "cpuset: Make cpuset hotplug synchronous"
  cgroupfs: Support user xattrs
  kernfs: Add option to enable user xattrs
  kernfs: Add removed_size out param for simple_xattr_set
  kernfs: kvmalloc xattr value instead of kmalloc
  cgroup: Restructure release_agent_path handling
  selftests/cgroup: add tests for cloning into cgroups
  clone3: allow spawning processes into cgroups
  cgroup: add cgroup_may_write() helper
  cgroup: refactor fork helpers
  cgroup: add cgroup_get_from_file() helper
  cgroup: unify attach permission checking
  cpuset: Make cpuset hotplug synchronous
  cgroup.c: Use built-in RCU list checking
  kselftest/cgroup: add cgroup destruction test
  cgroup: Clean up css_set task traversal

Documentation/admin-guide/cgroup-v1/cpusets.rst

@@ -223,6 +223,17 @@ cpu_online_mask using a CPU hotplug notifier, and the mems file
 automatically tracks the value of node_states[N_MEMORY]--i.e.,
 nodes with memory--using the cpuset_track_online_nodes() hook.
 
+The cpuset.effective_cpus and cpuset.effective_mems files are
+normally read-only copies of cpuset.cpus and cpuset.mems files
+respectively.  If the cpuset cgroup filesystem is mounted with the
+special "cpuset_v2_mode" option, the behavior of these files will become
+similar to the corresponding files in cpuset v2.  In other words, hotplug
+events will not change cpuset.cpus and cpuset.mems.  Those events will
+only affect cpuset.effective_cpus and cpuset.effective_mems which show
+the actual cpus and memory nodes that are currently used by this cpuset.
+See Documentation/admin-guide/cgroup-v2.rst for more information about
+cpuset v2 behavior.
+
 
 1.4 What are exclusive cpusets ?
 --------------------------------