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Commit 8ae121ac authored by Gregory Haskins's avatar Gregory Haskins Committed by Ingo Molnar
Browse files

sched: fix RT task-wakeup logic 

Dmitry Adamushko pointed out a logic error in task_wake_up_rt() where we
will always evaluate to "true".  You can find the thread here:

http://lkml.org/lkml/2008/4/22/296



In reality, we only want to try to push tasks away when a wake up request is
not going to preempt the current task.  So lets fix it.

Note: We introduce test_tsk_need_resched() instead of open-coding the flag
check so that the merge-conflict with -rt should help remind us that we
may need to support NEEDS_RESCHED_DELAYED in the future, too.

Signed-off-by: default avatarGregory Haskins <ghaskins@novell.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 983ed7a6

include/linux/sched.h

+6 −1
Original line number Diff line number Diff line
@@ -1977,6 +1977,11 @@ static inline void clear_tsk_need_resched(struct task_struct *tsk) 
	clear_tsk_thread_flag(tsk,TIF_NEED_RESCHED);

}



static inline int test_tsk_need_resched(struct task_struct *tsk)

{

	return unlikely(test_tsk_thread_flag(tsk,TIF_NEED_RESCHED));

}



static inline int signal_pending(struct task_struct *p)

{

	return unlikely(test_tsk_thread_flag(p,TIF_SIGPENDING));
@@ -1991,7 +1996,7 @@ static inline int fatal_signal_pending(struct task_struct *p) 


static inline int need_resched(void)

{

	return unlikely(test_thread_flag(TIF_NEED_RESCHED));

	return unlikely(test_tsk_need_resched(current));

}



/*

kernel/sched_rt.c

+5 −2
Original line number Diff line number Diff line
@@ -1098,11 +1098,14 @@ static void post_schedule_rt(struct rq *rq) 
	}

}





/*

 * If we are not running and we are not going to reschedule soon, we should

 * try to push tasks away now

 */

static void task_wake_up_rt(struct rq *rq, struct task_struct *p)

{

	if (!task_running(rq, p) &&

	    (p->prio >= rq->rt.highest_prio) &&

	    !test_tsk_need_resched(rq->curr) &&

	    rq->rt.overloaded)

		push_rt_tasks(rq);

}