Messages in this thread Patch in this message | | | Date | Sat, 18 Sep 2010 11:58:55 -0700 | From | Greg KH <> | Subject | [091/123] sched: Queue a deboosted task to the head of the RT prio queue |
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From: Thomas Gleixner <tglx@linutronix.de>
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 <mathias.weber.mw1@roche.com> Reported-by: Carsten Emde <cbe@osadl.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Carsten Emde <cbe@osadl.org> Tested-by: Mathias Weber <mathias.weber.mw1@roche.com> LKML-Reference: <20100120171629.809074113@linutronix.de> Signed-off-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> --- 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); }
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