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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, juri.lelli@arm.com, rostedt@goodmis.org,
	xlpang@redhat.com, bigeasy@linutronix.de,
	linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com,
	jdesfossez@efficios.com, bristot@redhat.com
Subject: Re: [RFC][PATCH 4/4] futex: Rewrite FUTEX_UNLOCK_PI
Date: Sat, 8 Oct 2016 19:06:04 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.20.1610081903550.5222@nanos> (raw)
In-Reply-To: <20161008165540.GI3568@worktop.programming.kicks-ass.net>

On Sat, 8 Oct 2016, Peter Zijlstra wrote:
> > So in this case we tell the caller on CPU 1 that the futex is in
> > inconsistent state, because pistate->owner still points to the unlocking
> > task while the user space value alread shows the new owner. So this sanity
> > check triggers and we simply fail while we should not. It's [10] in the
> > state matrix above attach_to_pi_state().
> 
> Urgh, yes. I think I can cure that, by taking
> pi_state->pi_mutex.wait_lock in attach_to_pi_state(), but blergh.
> 
> > I suspect that there are more issues like this, especially since I did not
> > look at requeue_pi yet, but by now my brain is completely fried.
> 
> Yes, I know about fried brains :-( This stuff has far too many moving
> parts. I've been staring at this stuff far too long.
> 
> Also, we need better tools to stress this stuff.

I tried to come up with something which forces all corner cases of this
years ago and failed. The state space seems to be infinite.

Thanks,

	tglx

  reply	other threads:[~2016-10-08 17:08 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-03  9:12 [RFC][PATCH 0/4] FUTEX_UNLOCK_PI wobbles Peter Zijlstra
2016-10-03  9:12 ` [RFC][PATCH 1/4] futex: Cleanup variable names for futex_top_waiter() Peter Zijlstra
2016-10-03 14:15   ` Steven Rostedt
2016-10-05  3:58   ` Davidlohr Bueso
2016-10-03  9:12 ` [RFC][PATCH 2/4] futex: Use smp_store_release() in mark_wake_futex() Peter Zijlstra
2016-10-03 14:19   ` Steven Rostedt
2016-10-05  3:57   ` Davidlohr Bueso
2016-10-05  6:20     ` Peter Zijlstra
2016-10-03  9:12 ` [RFC][PATCH 3/4] futex: Remove rt_mutex_deadlock_account_*() Peter Zijlstra
2016-10-03  9:34   ` Peter Zijlstra
2016-10-03 14:25   ` Steven Rostedt
2016-10-05  1:08   ` Davidlohr Bueso
2016-10-05  7:29   ` Sebastian Andrzej Siewior
2016-10-03  9:12 ` [RFC][PATCH 4/4] futex: Rewrite FUTEX_UNLOCK_PI Peter Zijlstra
2016-10-03 15:36   ` Steven Rostedt
2016-10-03 15:44     ` Peter Zijlstra
2016-10-03 15:45     ` Peter Zijlstra
2016-10-03 16:23       ` Steven Rostedt
2016-10-05  7:41   ` Sebastian Andrzej Siewior
2016-10-05  8:09     ` Peter Zijlstra
2016-10-05  8:21       ` Sebastian Andrzej Siewior
2016-10-05  8:32         ` Peter Zijlstra
2016-10-06 10:29   ` Peter Zijlstra
2016-10-07 11:21   ` Peter Zijlstra
2016-10-08 15:53     ` Thomas Gleixner
2016-10-08 16:55       ` Peter Zijlstra
2016-10-08 17:06         ` Thomas Gleixner [this message]
2016-10-10 10:17         ` Thomas Gleixner
2016-10-10 11:40           ` Peter Zijlstra
2016-10-21 12:27           ` Peter Zijlstra
2016-10-27 20:36             ` Thomas Gleixner
2016-11-23 19:20               ` Peter Zijlstra
2016-11-24 16:52                 ` Peter Zijlstra
2016-11-24 17:56                   ` Thomas Gleixner
2016-11-24 18:58                     ` Peter Zijlstra
2016-11-25  9:23                       ` Peter Zijlstra
2016-11-25 10:03                         ` Peter Zijlstra
2016-11-25 19:13                           ` Thomas Gleixner
2016-11-25 14:09               ` Peter Zijlstra
2016-10-08 18:22     ` Thomas Gleixner
2016-10-09 11:17     ` Thomas Gleixner
2016-10-10 14:06       ` Peter Zijlstra
2016-10-05  1:02 ` [RFC][PATCH 0/4] FUTEX_UNLOCK_PI wobbles Davidlohr Bueso
2016-10-05  6:20   ` Peter Zijlstra
2016-10-05  7:26     ` Sebastian Andrzej Siewior
2016-10-05 16:04     ` Davidlohr Bueso

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