From: Juri Lelli <juri.lelli@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, tglx@linutronix.de, rostedt@goodmis.org,
xlpang@redhat.com, linux-kernel@vger.kernel.org,
mathieu.desnoyers@efficios.com, jdesfossez@efficios.com,
bristot@redhat.com
Subject: Re: [RFC][PATCH 6/8] sched/rtmutex: Refactor rt_mutex_setprio()
Date: Tue, 14 Jun 2016 14:14:24 +0100 [thread overview]
Message-ID: <20160614131424.GK5981@e106622-lin> (raw)
In-Reply-To: <20160607200215.990237037@infradead.org>
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) <peterz@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
next prev parent reply other threads:[~2016-06-14 13:14 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-07 19:56 [RFC][PATCH 0/8] PI and assorted failings Peter Zijlstra
2016-06-07 19:56 ` [RFC][PATCH 1/8] rtmutex: Deboost before waking up the top waiter Peter Zijlstra
2016-06-14 9:09 ` Juri Lelli
2016-06-14 12:54 ` Peter Zijlstra
2016-06-14 13:20 ` Juri Lelli
2016-06-14 13:59 ` Peter Zijlstra
2016-06-14 16:36 ` Davidlohr Bueso
2016-06-14 17:01 ` Juri Lelli
2016-06-14 18:22 ` Steven Rostedt
2016-06-07 19:56 ` [RFC][PATCH 2/8] sched/rtmutex/deadline: Fix a PI crash for deadline tasks Peter Zijlstra
2016-06-14 10:21 ` Juri Lelli
2016-06-14 12:30 ` Peter Zijlstra
2016-06-14 12:53 ` Xunlei Pang
2016-06-14 13:07 ` Juri Lelli
2016-06-14 16:39 ` Juri Lelli
2016-06-14 18:42 ` Steven Rostedt
2016-06-14 20:28 ` Peter Zijlstra
2016-06-15 16:14 ` Steven Rostedt
2016-06-07 19:56 ` [RFC][PATCH 3/8] sched/deadline/rtmutex: Dont miss the dl_runtime/dl_period update Peter Zijlstra
2016-06-14 10:43 ` Juri Lelli
2016-06-14 12:09 ` Peter Zijlstra
2016-06-15 16:30 ` Steven Rostedt
2016-06-15 17:55 ` Peter Zijlstra
2016-06-07 19:56 ` [RFC][PATCH 4/8] rtmutex: Remove rt_mutex_fastunlock() Peter Zijlstra
2016-06-15 16:43 ` Steven Rostedt
2016-06-07 19:56 ` [RFC][PATCH 5/8] rtmutex: Clean up Peter Zijlstra
2016-06-14 12:08 ` Juri Lelli
2016-06-14 12:32 ` Peter Zijlstra
2016-06-14 12:41 ` Juri Lelli
2016-06-07 19:56 ` [RFC][PATCH 6/8] sched/rtmutex: Refactor rt_mutex_setprio() Peter Zijlstra
2016-06-14 13:14 ` Juri Lelli [this message]
2016-06-14 14:08 ` Peter Zijlstra
2016-06-07 19:56 ` [RFC][PATCH 7/8] sched,tracing: Update trace_sched_pi_setprio() Peter Zijlstra
2016-06-07 19:56 ` [RFC][PATCH 8/8] rtmutex: Fix PI chain order integrity Peter Zijlstra
2016-06-14 17:39 ` Juri Lelli
2016-06-14 19:44 ` Peter Zijlstra
2016-06-15 7:25 ` Juri Lelli
2016-06-27 12:23 ` Peter Zijlstra
2016-06-27 12:40 ` Thomas Gleixner
2016-06-28 9:05 ` Juri Lelli
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