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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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10
kernel/workqueue.c
View file

@ -1757,12 +1757,8 @@ static struct worker *create_worker(struct worker_pool *pool)
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 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
}
wq->rescuer = rescuer;
rescuer->task->flags |= PF_THREAD_BOUND;
rescuer->task->flags |= PF_NO_SETAFFINITY;
wake_up_process(rescuer->task);
}