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sched: Handle priority boosted tasks proper in setscheduler()

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Ronny reported that the following scenario is not handled correctly:

	T1 (prio = 10)
	   lock(rtmutex);

	T2 (prio = 20)
	   lock(rtmutex)
	      boost T1

	T1 (prio = 20)
	   sys_set_scheduler(prio = 30)
	   T1 prio = 30
	   ....
	   sys_set_scheduler(prio = 10)
	   T1 prio = 30

The last step is wrong as T1 should now be back at prio 20.

Commit c365c292d0 ("sched: Consider pi boosting in setscheduler()")
only handles the case where a boosted tasks tries to lower its
priority.

Fix it by taking the new effective priority into account for the
decision whether a change of the priority is required.

Reported-by: Ronny Meeus <ronny.meeus@gmail.com>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: <stable@vger.kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Fixes: c365c292d0 ("sched: Consider pi boosting in setscheduler()")
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1505051806060.4225@nanos
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Thomas Gleixner 2015-05-05 19:49:49 +02:00 • committed by Ingo Molnar
parent 3e0283a53f
commit 0782e63bc6
3 changed files with 25 additions and 20 deletions
Download patch file Download diff file Expand all files Collapse all files

12
kernel/locking/rtmutex.c
View file

@ -265,15 +265,17 @@ struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
}
/*
* Called by sched_setscheduler() to check whether the priority change
* is overruled by a possible priority boosting.
* Called by sched_setscheduler() to get the priority which will be
* effective after the change.
*/
int rt_mutex_check_prio(struct task_struct *task, int newprio)
int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
{
if (!task_has_pi_waiters(task))
return 0;
return newprio;
return task_top_pi_waiter(task)->task->prio <= newprio;
if (task_top_pi_waiter(task)->task->prio <= newprio)
return task_top_pi_waiter(task)->task->prio;
return newprio;
}
/*