From: Thomas Gleixner commit 60db48cacb9b253d5607a5ff206112a59cd09e34 upstream rtmutex_set_prio() is used to implement priority inheritance for futexes. When a task is deboosted it gets enqueued at the tail of its RT priority list. This is violating the POSIX scheduling semantics: rt priority list X contains two runnable tasks A and B task A runs with priority X and holds mutex M task C preempts A and is blocked on mutex M -> task A is boosted to priority of task C (Y) task A unlocks the mutex M and deboosts itself -> A is dequeued from rt priority list Y -> A is enqueued to the tail of rt priority list X task C schedules away task B runs This is wrong as task A did not schedule away and therefor violates the POSIX scheduling semantics. Enqueue the task to the head of the priority list instead. Reported-by: Mathias Weber Reported-by: Carsten Emde Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Tested-by: Carsten Emde Tested-by: Mathias Weber LKML-Reference: <20100120171629.809074113@linutronix.de> Signed-off-by: Mike Galbraith Signed-off-by: Greg Kroah-Hartman --- kernel/sched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/sched.c +++ b/kernel/sched.c @@ -6184,7 +6184,7 @@ void rt_mutex_setprio(struct task_struct if (running) p->sched_class->set_curr_task(rq); if (on_rq) { - enqueue_task(rq, p, 0, false); + enqueue_task(rq, p, 0, oldprio < prio); check_class_changed(rq, p, prev_class, oldprio, running); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/