Ingo or Tglx,
It has come to my attention that the dynamic hrtimer softirq can lose a
boosted priority. That is, if a softirq is running while a timeout
happens, and the call back is of lower priority than the currently
running hrtimer softirq, the timer interrupt will still lower the
hrtimer softirq.
Here's the problem code:
static void wakeup_softirqd_prio(int softirq, int prio)
{
/* Interrupts are disabled: no need to stop preemption */
struct task_struct *tsk = __get_cpu_var(ksoftirqd[softirq].tsk);
if (tsk) {
if (tsk->normal_prio != prio) {
struct sched_param param;
param.sched_priority = MAX_RT_PRIO-1 - prio;
setscheduler(tsk, -1, SCHED_FIFO, ¶m);
}
if(tsk->state != TASK_RUNNING)
wake_up_process(tsk);
}
}
So, tsk could be softirqd-hrmono and we lower the priority. (only
normal_prio is checked versus prio).
So this can be a problem, if the softirq function holds a lock of a high
priority task, and is running boosted. If another timer goes off with a
lower priority, we can lower the priority of the softirqd and lose the
inherited priority that it was running at.
-- Steve
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