kthreads: simplify migration_thread() exit path

Now that kthread_stop() can be used even if the task has already exited, we can kill the "wait_to_die:" loop in migration_thread(). But we must pin rq->migration_thread after creation. Actually, I don't think CPU_UP_CANCELED or CPU_DEAD should wait for ->migration_thread exit. Perhaps we can simplify this code a bit more. migration_call() can set ->should_stop and forget about this thread. But we need a new helper in kthred.c for that. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Pavel Emelyanov <xemul@openvz.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Vitaliy Gusev <vgusev@openvz.org Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kthreads: simplify migration_thread() exit path
Now that kthread_stop() can be used even if the task has already exited, we can kill the "wait_to_die:" loop in migration_thread(). But we must pin rq->migration_thread after creation. Actually, I don't think CPU_UP_CANCELED or CPU_DEAD should wait for ->migration_thread exit. Perhaps we can simplify this code a bit more. migration_call() can set ->should_stop and forget about this thread. But we need a new helper in kthred.c for that. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Pavel Emelyanov <xemul@openvz.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Vitaliy Gusev <vgusev@openvz.org Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Oleg Nesterov · Linus Torvalds
1 parent 63706172f3
Showing 1 changed file with 4 additions and 10 deletions Side-by-side Diff
kernel/sched.c
@@ -7045,7 +7045,7 @@
  
 		if (cpu_is_offline(cpu)) {
 			spin_unlock_irq(&rq->lock);
-			goto wait_to_die;
+			break;
 		}
  
 		if (rq->active_balance) {
  
@@ -7071,16 +7071,7 @@
 		complete(&req->done);
 	}
 	__set_current_state(TASK_RUNNING);
-	return 0;
  
-wait_to_die:
-	/* Wait for kthread_stop */
-	set_current_state(TASK_INTERRUPTIBLE);
-	while (!kthread_should_stop()) {
-		schedule();
-		set_current_state(TASK_INTERRUPTIBLE);
-	}
-	__set_current_state(TASK_RUNNING);
 	return 0;
 }
  
@@ -7494,6 +7485,7 @@
 		rq = task_rq_lock(p, &flags);
 		__setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
 		task_rq_unlock(rq, &flags);
+		get_task_struct(p);
 		cpu_rq(cpu)->migration_thread = p;
 		break;
  
@@ -7524,6 +7516,7 @@
 		kthread_bind(cpu_rq(cpu)->migration_thread,
 			     cpumask_any(cpu_online_mask));
 		kthread_stop(cpu_rq(cpu)->migration_thread);
+		put_task_struct(cpu_rq(cpu)->migration_thread);
 		cpu_rq(cpu)->migration_thread = NULL;
 		break;
  
@@ -7533,6 +7526,7 @@
 		migrate_live_tasks(cpu);
 		rq = cpu_rq(cpu);
 		kthread_stop(rq->migration_thread);
+		put_task_struct(rq->migration_thread);
 		rq->migration_thread = NULL;
 		/* Idle task back to normal (off runqueue, low prio) */
 		spin_lock_irq(&rq->lock);
...	...	@@ -7045,7 +7045,7 @@
7045	7045
7046	7046	if (cpu_is_offline(cpu)) {
7047	7047	spin_unlock_irq(&rq->lock);
7048		- goto wait_to_die;
	7048	+ break;
7049	7049	}
7050	7050
7051	7051	if (rq->active_balance) {
7052	7052
...	...	@@ -7071,16 +7071,7 @@
7071	7071	complete(&req->done);
7072	7072	}
7073	7073	__set_current_state(TASK_RUNNING);
7074		- return 0;
7075	7074
7076		-wait_to_die:
7077		- /* Wait for kthread_stop */
7078		- set_current_state(TASK_INTERRUPTIBLE);
7079		- while (!kthread_should_stop()) {
7080		- schedule();
7081		- set_current_state(TASK_INTERRUPTIBLE);
7082		- }
7083		- __set_current_state(TASK_RUNNING);
7084	7075	return 0;
7085	7076	}
7086	7077
...	...	@@ -7494,6 +7485,7 @@
7494	7485	rq = task_rq_lock(p, &flags);
7495	7486	__setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
7496	7487	task_rq_unlock(rq, &flags);
	7488	+ get_task_struct(p);
7497	7489	cpu_rq(cpu)->migration_thread = p;
7498	7490	break;
7499	7491
...	...	@@ -7524,6 +7516,7 @@
7524	7516	kthread_bind(cpu_rq(cpu)->migration_thread,
7525	7517	cpumask_any(cpu_online_mask));
7526	7518	kthread_stop(cpu_rq(cpu)->migration_thread);
	7519	+ put_task_struct(cpu_rq(cpu)->migration_thread);
7527	7520	cpu_rq(cpu)->migration_thread = NULL;
7528	7521	break;
7529	7522
...	...	@@ -7533,6 +7526,7 @@
7533	7526	migrate_live_tasks(cpu);
7534	7527	rq = cpu_rq(cpu);
7535	7528	kthread_stop(rq->migration_thread);
	7529	+ put_task_struct(rq->migration_thread);
7536	7530	rq->migration_thread = NULL;
7537	7531	/* Idle task back to normal (off runqueue, low prio) */
7538	7532	spin_lock_irq(&rq->lock);