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, 2 insertions, 2 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a32f9432666c..3852d926322c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2224,11 +2224,11 @@ retry_find_task:
                 tsk = tsk->group_leader;
 
         /*
-         * Workqueue threads may acquire PF_THREAD_BOUND and become
+         * Workqueue threads may acquire PF_NO_SETAFFINITY and become
          * trapped in a cpuset, or RT worker may be born in a cgroup
          * with no rt_runtime allocated.  Just say no.
          */
-        if (tsk == kthreadd_task || (tsk->flags & PF_THREAD_BOUND)) {
+        if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
                 ret = -EINVAL;
                 rcu_read_unlock();
                 goto out_unlock_cgroup;