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Commit aa44002e authored by Zhang Qiao's avatar Zhang Qiao Committed by Greg Kroah-Hartman
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cpuset: Fix unsafe lock order between cpuset lock and cpuslock 



The backport commit 4eec5fe1 ("cgroup/cpuset: Fix a race
between cpuset_attach() and cpu hotplug") looks suspicious since
it comes before commit d74b27d63a8b ("cgroup/cpuset: Change
cpuset_rwsem and hotplug lock order") v5.4-rc1~176^2~30 when
the locking order was: cpuset lock, cpus lock.

Fix it with the correct locking order and reduce the cpus locking
range because only set_cpus_allowed_ptr() needs the protection of
cpus lock.

Fixes: 4eec5fe1 ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug")
Reported-by: default avatarMichal Koutný <mkoutny@suse.com>
Signed-off-by: default avatarZhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1ba1ec19

kernel/cgroup/cpuset.c

+6 −2
Original line number Diff line number Diff line
@@ -1528,9 +1528,13 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
	cgroup_taskset_first(tset, &css);

	cs = css_cs(css);



	cpus_read_lock();

	mutex_lock(&cpuset_mutex);



	/*

	 * It should hold cpus lock because a cpu offline event can

	 * cause set_cpus_allowed_ptr() failed.

	 */

	get_online_cpus();

	/* prepare for attach */

	if (cs == &top_cpuset)

		cpumask_copy(cpus_attach, cpu_possible_mask);
@@ -1549,6 +1553,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
		cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);

		cpuset_update_task_spread_flag(cs, task);

	}

       put_online_cpus();



	/*

	 * Change mm for all threadgroup leaders. This is expensive and may
@@ -1584,7 +1589,6 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
		wake_up(&cpuset_attach_wq);



	mutex_unlock(&cpuset_mutex);

	cpus_read_unlock();

}



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