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

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kernel/workqueue.c+3−7

 	set_user_nice(worker->task, pool->attrs->nice);
 	set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
-	/*
+	/* prevent userland from meddling with cpumask of workqueue workers */
-	 * %PF_THREAD_BOUND is used to prevent userland from meddling with
+	worker->task->flags |= PF_NO_SETAFFINITY;
-	 * cpumask of workqueue workers.  This is an abuse.  We need
-	 * %PF_NO_SETAFFINITY.
-	 */
-	worker->task->flags |= PF_THREAD_BOUND;
 	/*
 	 * The caller is responsible for ensuring %POOL_DISASSOCIATED
 		}
 		wq->rescuer = rescuer;
-		rescuer->task->flags |= PF_THREAD_BOUND;
+		rescuer->task->flags |= PF_NO_SETAFFINITY;
 		wake_up_process(rescuer->task);
 	}