Hi,
still digesting this change, but I'll point out below why I think you
are hitting a NULL ptr dereference (discussed on IRC).
On 07/06/16 21:56, Peter Zijlstra wrote:
> With the introduction of SCHED_DEADLINE the whole notion that priority
> is a single number is gone, therefore the @prio argument to
> rt_mutex_setprio() doesn't make sense anymore.
>
> So rework the code to pass a pi_task instead.
>
> Note this also fixes a problem with pi_top_task caching; previously we
> would not set the pointer (call rt_mutex_update_top_task) if the
> priority didn't change, this could lead to a stale pointer.
>
> As for the XXX, I think its fine to use pi_task->prio, because if it
> differs from waiter->prio, a PI chain update is immenent.
>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> ---
> include/linux/sched/rt.h | 21 +-------
> kernel/locking/rtmutex.c | 105
> +++++++++++-----------------------------
> kernel/locking/rtmutex_common.h | 1
> kernel/sched/core.c | 66 ++++++++++++++++++++-----
> 4 files changed, 88 insertions(+), 105 deletions(-)
>
[...]
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -256,61 +256,16 @@ rt_mutex_dequeue_pi(struct task_struct *
> RB_CLEAR_NODE(&waiter->pi_tree_entry);
> }
>
> -void rt_mutex_update_top_task(struct task_struct *p)
> +static void rt_mutex_adjust_prio(struct task_struct *p)
> {
> - if (!task_has_pi_waiters(p)) {
> - p->pi_top_task = NULL;
> - return;
> - }
> + struct task_struct *pi_task = NULL;
>
> - p->pi_top_task = task_top_pi_waiter(p)->task;
> -}
> -
> -/*
> - * Calculate task priority from the waiter tree priority
> - *
> - * Return task->normal_prio when the waiter tree is empty or when
> - * the waiter is not allowed to do priority boosting
> - */
> -int rt_mutex_getprio(struct task_struct *task)
> -{
> - if (likely(!task_has_pi_waiters(task)))
> - return task->normal_prio;
> + lockdep_assert_held(&p->pi_lock);
>
> - return min(task_top_pi_waiter(task)->prio,
> - task->normal_prio);
> -}
> + if (!task_has_pi_waiters(p))
Shouldn't this be the other way around?
if (task_has_pi_waiters(p))
pi_task = ...
Best,
- Juri
