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.

Tejun Heo committed 13 years ago

Commit 14a40ff1 parent 2e109a26 files · +19 −24Browse files

Showing the changes to kernel/workqueue.c (1 of 6 files). Show all

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kernel/workqueue.c+3−7

@@ -1757,12 +1757,8 @@ static struct worker create_worker(struct worker_pool pool) · 1756 unmodified lines
1757	1757	set_user_nice(worker->task, pool->attrs->nice);
1758	1758	set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
1759	1759
1760		− /*
1761		− * %PF_THREAD_BOUND is used to prevent userland from meddling with
1762		− * cpumask of workqueue workers. This is an abuse. We need
1763		− * %PF_NO_SETAFFINITY.
1764		− */
1765		− worker->task->flags \|= PF_THREAD_BOUND;
	1760	+ /* prevent userland from meddling with cpumask of workqueue workers */
	1761	+ worker->task->flags \|= PF_NO_SETAFFINITY;
1766	1762
1767	1763	/*
1768	1764	* The caller is responsible for ensuring %POOL_DISASSOCIATED
@@ -3876,7 +3872,7 @@ struct workqueue_struct __alloc_workqueue_key(const char fmt, · 2107 unmodified lines
3876	3872	}
3877	3873
3878	3874	wq->rescuer = rescuer;
3879		− rescuer->task->flags \|= PF_THREAD_BOUND;
	3875	+ rescuer->task->flags \|= PF_NO_SETAFFINITY;
3880	3876	wake_up_process(rescuer->task);
3881	3877	}
3882	3878