linux-kernel - [patch] BFS 421: change task cpu with runqueue lock held

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Date:	Fri, 15 Jun 2012 20:15:50 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	Hillf Danton <dhillf@...il.com>
Subject: [patch] BFS 421: change task cpu with runqueue lock held

Set tasks cpu after grabbing runqueue lock.


--- a/kernel/sched/bfs.c	Fri Jun 15 19:57:30 2012
+++ b/kernel/sched/bfs.c	Fri Jun 15 20:00:52 2012
@@ -1031,11 +1031,10 @@ void set_task_cpu(struct task_struct *p,
 	WARN_ON_ONCE(debug_locks && !lockdep_is_held(&grq.lock));
 #endif
 	trace_sched_migrate_task(p, cpu);
-	if (task_cpu(p) != cpu)
-		perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, NULL, 0);
-
-	if (task_thread_info(p)->cpu != cpu)
+	if (task_cpu(p) != cpu) {
 		task_thread_info(p)->cpu = cpu;
+		perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, NULL, 0);
+	}
 }

 static inline void clear_sticky(struct task_struct *p)
@@ -1638,7 +1637,6 @@ void sched_fork(struct task_struct *p)
 	 * event cannot wake it up and insert it on the runqueue either.
 	 */
 	p->state = TASK_RUNNING;
-	set_task_cpu(p, cpu);

 	/* Should be reset in fork.c but done here for ease of bfs patching */
 	p->sched_time = p->stime_pc = p->utime_pc = 0;
@@ -1688,8 +1686,6 @@ void sched_fork(struct task_struct *p)
 	/* Want to start with kernel preemption disabled. */
 	task_thread_info(p)->preempt_count = 1;
 #endif
-	if (unlikely(p->policy == SCHED_FIFO))
-		goto out;
 	/*
 	 * Share the timeslice between parent and child, thus the
 	 * total amount of pending timeslices in the system doesn't change,
@@ -1700,6 +1696,9 @@ void sched_fork(struct task_struct *p)
 	 * is always equal to current->deadline.
 	 */
 	rq = task_grq_lock_irq(curr);
+	set_task_cpu(p, cpu);
+	if (unlikely(p->policy == SCHED_FIFO))
+		goto out;
 	if (likely(rq->rq_time_slice >= RESCHED_US * 2)) {
 		rq->rq_time_slice /= 2;
 		p->time_slice = rq->rq_time_slice;
@@ -1715,8 +1714,8 @@ void sched_fork(struct task_struct *p)
 		time_slice_expired(p);
 	}
 	p->last_ran = rq->rq_last_ran;
-	task_grq_unlock_irq();
 out:
+	task_grq_unlock_irq();
 	put_cpu();
 }

--
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