From: Peter Zijlstra <peterz@infradead.org>
To: Juri Lelli <juri.lelli@arm.com>
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, Ingo Molnar <mingo@redhat.com>
Subject: Re: [RFC][PATCH 2/8] sched/rtmutex/deadline: Fix a PI crash for deadline tasks
Date: Tue, 14 Jun 2016 14:30:23 +0200 [thread overview]
Message-ID: <20160614123023.GG30921@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160614102109.GF5981@e106622-lin>
On Tue, Jun 14, 2016 at 11:21:09AM +0100, Juri Lelli wrote:
> > [XXX this next section is unparsable]
>
> Yes, a bit hard to understand. However, am I correct in assuming this
> patch and the previous one should fix this problem? Or are there still
> other races causing issues?
I think so; so there were two related problems,
1) top_waiter was used outside its serialization
2) a race against the top waiter task and sched_setscheduler() changing
its state
Now, I could not understand a word of that marked paragraph, but from my
understanding of the code both are solved.
1) by keeping the top_pi_task cache updated under pi_lock and rq->lock,
thereby ensuring that holding either is sufficient to stabilize it.
2) sched_setscheduler() can change the parameters of the top_pi_task,
but since it too holds both pi_lock and rq->lock, it cannot happen at
the same time that we're looking at the cached top pi waiter pointer
thingy.
It can however happen that top_pi_waiter is not in fact the top waiter
in a narrow window between sched_setscheduler() changing its parameters
and rt_mutex_adjust_pi() re-ordering the PI chain - ending in updating
the cached top task pointer thingy.
next prev parent reply other threads:[~2016-06-14 12:30 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 [this message]
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
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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