sched: prevent bound kthreads from changing cpus_allowed

Kthreads that have called kthread_bind() are bound to specific cpus, so
other tasks should not be able to change their cpus_allowed from under
them.  Otherwise, it is possible to move kthreads, such as the migration
or software watchdog threads, so they are not allowed access to the cpu
they work on.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index e9c24a128655..164fe7fe0d89 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5563,6 +5563,12 @@ int set_cpus_allowed_ptr(struct task_struct *p, const cpumask_t *new_mask)
                 goto out;
         }
 
+        if (unlikely((p->flags & PF_THREAD_BOUND) && p != current &&
+                     !cpus_equal(p->cpus_allowed, *new_mask))) {
+                ret = -EINVAL;
+                goto out;
+        }
+
         if (p->sched_class->set_cpus_allowed)
                 p->sched_class->set_cpus_allowed(p, new_mask);
         else {