tree eed1f4edce9839509eb26a2365bdcc7ef5d26eff
parent 452477fa68c6d8ef80adebd05194c1c157ad9a53
author Tejun Heo <tj@kernel.org> 1357577468 -0800
committer Tejun Heo <tj@kernel.org> 1357577468 -0800

cpuset: schedule hotplug propagation from cpuset_attach() if the cpuset is empty

cpuset is scheduled to be decoupled from cgroup_lock which will make
hotplug handling race with task migration.  cpus or mems will be
allowed to go offline between ->can_attach() and ->attach().  If
hotplug takes down all cpus or mems of a cpuset while attach is in
progress, ->attach() may end up putting tasks into an empty cpuset.

This patchset makes ->attach() schedule hotplug propagation if the
cpuset is empty after attaching is complete.  This will move the tasks
to the nearest ancestor which can execute and the end result would be
as if hotplug handling happened after the tasks finished attaching.

cpuset_write_resmask() now also flushes cpuset_propagate_hotplug_wq to
wait for propagations scheduled directly by cpuset_attach().

This currently doesn't make any functional difference as everything is
protected by cgroup_mutex but enables decoupling the locking.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>