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>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 969be0b..39a591f 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1757,12 +1757,8 @@
set_user_nice(worker->task, pool->attrs->nice);
set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
- /*
- * %PF_THREAD_BOUND is used to prevent userland from meddling with
- * cpumask of workqueue workers. This is an abuse. We need
- * %PF_NO_SETAFFINITY.
- */
- worker->task->flags |= PF_THREAD_BOUND;
+ /* prevent userland from meddling with cpumask of workqueue workers */
+ worker->task->flags |= PF_NO_SETAFFINITY;
/*
* The caller is responsible for ensuring %POOL_DISASSOCIATED
@@ -3876,7 +3872,7 @@
}
wq->rescuer = rescuer;
- rescuer->task->flags |= PF_THREAD_BOUND;
+ rescuer->task->flags |= PF_NO_SETAFFINITY;
wake_up_process(rescuer->task);
}