sched: replace PF_THREAD_BOUND with PF_NO_SETAFFINITY

PF_THREAD_BOUND was originally used to mark kernel threads which were
bound to a specific CPU using kthread_bind() and a task with the flag
set allows cpus_allowed modifications only to itself.  Workqueue is
currently abusing it to prevent userland from meddling with
cpus_allowed of workqueue workers.

What we need is a flag to prevent userland from messing with
cpus_allowed of certain kernel tasks.  In kernel, anyone can
(incorrectly) squash the flag, and, for worker-type usages,
restricting cpus_allowed modification to the task itself doesn't
provide meaningful extra proection as other tasks can inject work
items to the task anyway.

This patch replaces PF_THREAD_BOUND with PF_NO_SETAFFINITY.
sched_setaffinity() checks the flag and return -EINVAL if set.
set_cpus_allowed_ptr() is no longer affected by the flag.

This will allow simplifying workqueue worker CPU affinity management.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 8 insertions, 8 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 4f9dfe43ecbd..f22e94792707 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1388,16 +1388,16 @@ static int cpuset_can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
 
         cgroup_taskset_for_each(task, cgrp, tset) {
                 /*
-                 * Kthreads bound to specific cpus cannot be moved to a new
-                 * cpuset; we cannot change their cpu affinity and
-                 * isolating such threads by their set of allowed nodes is
-                 * unnecessary.  Thus, cpusets are not applicable for such
-                 * threads.  This prevents checking for success of
-                 * set_cpus_allowed_ptr() on all attached tasks before
-                 * cpus_allowed may be changed.
+                 * Kthreads which disallow setaffinity shouldn't be moved
+                 * to a new cpuset; we don't want to change their cpu
+                 * affinity and isolating such threads by their set of
+                 * allowed nodes is unnecessary.  Thus, cpusets are not
+                 * applicable for such threads.  This prevents checking for
+                 * success of set_cpus_allowed_ptr() on all attached tasks
+                 * before cpus_allowed may be changed.
                  */
                 ret = -EINVAL;
-                if (task->flags & PF_THREAD_BOUND)
+                if (task->flags & PF_NO_SETAFFINITY)
                         goto out_unlock;
                 ret = security_task_setscheduler(task);
                 if (ret)