cpuset: Check if the cpus allowed is a subset of the cpuset's cpusfor PF_THREAD_BOUND threads

[Dhaval Giani]

When a kernel thread which has been bound to a CPU is moved to
a cpuset which is a superset of the CPU it is bound to, the
movement fails.

[root@llm11 cgroups]# mkdir a
[root@llm11 cgroups]# echo 3 > a/cpuset.cpus
[root@llm11 cgroups]# echo 0 > a/cpuset.mems
[root@llm11 cgroups]# echo 12 > a/tasks
[root@llm11 cgroups]# echo 12 > tasks
-bash: echo: write error: Invalid argument
[root@llm11 cgroups]# cat cpuset.cpus
0-7
[root@llm11 cgroups]#

(pid 12 is the migration thread bound to CPU 3)

Change the check to see if the cpus allowed is a subset of the
cpus allowed for that cpuset.

Signed-off-by: Dhaval Giani <dhaval@xxxxxxxxxxxxxxxxxx>
---
 kernel/cpuset.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1362,7 +1362,7 @@ static int cpuset_can_attach(struct cgro
 
 	if (tsk->flags & PF_THREAD_BOUND) {
 		mutex_lock(&callback_mutex);
-		if (!cpumask_equal(&tsk->cpus_allowed, cs->cpus_allowed))
+		if (!cpumask_subset(&tsk->cpus_allowed, cs->cpus_allowed))
 			ret = -EINVAL;
 		mutex_unlock(&callback_mutex);
 	}
-- 
regards,
Dhaval
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