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sched: replace PF_THREAD_BOUND with PF_NO_SETAFFINITY

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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>
This commit is contained in:
Tejun Heo
2013-03-19 13:45:20 -07:00
parent 2e109a2855
commit 14a40ffccd
6 changed files with 19 additions and 24 deletions
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16
kernel/cpuset.c
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@@ -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)