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From: Chris Wilson <chris@chris-wilson.co.uk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, tglx@linutronix.de,
	linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	paulmck@kernel.org, frederic@kernel.org,
	torvalds@linux-foundation.org, hch@lst.de
Subject: Re: [PATCH -v2 1/5] sched: Fix ttwu() race
Date: Thu, 23 Jul 2020 20:41:03 +0100	[thread overview]
Message-ID: <159553326368.21069.3167204000119437062@build.alporthouse.com> (raw)
In-Reply-To: <20200723182841.GS10769@hirez.programming.kicks-ass.net>

Quoting Peter Zijlstra (2020-07-23 19:28:41)
> On Wed, Jul 22, 2020 at 10:57:56AM +0100, Chris Wilson wrote:
> 
> > Perhaps more damning is that I can replace WF_ON_CPU with p->on_cpu to
> > suppress the warning:
> 
> *argh*, I'm starting to go mad...
> 
> Chris, could you please try the below patch?

 ttwu-IPI-self: 1==1, p->on_cpu=0;0, task_cpu(p)=1;1
 ttwu-IPI-self: 1==1, p->on_cpu=0;0, task_cpu(p)=1;1
 ttwu-IPI-self: 0==0, p->on_cpu=0;0, task_cpu(p)=0;0
 ttwu-IPI-self: 3==3, p->on_cpu=0;0, task_cpu(p)=3;3
 ttwu-IPI-self: 2==2, p->on_cpu=0;0, task_cpu(p)=2;2
 ttwu-IPI-self: 1==1, p->on_cpu=0;0, task_cpu(p)=1;1
 ttwu-IPI-self: 2==2, p->on_cpu=0;0, task_cpu(p)=2;2
 ttwu-IPI-self: 2==2, p->on_cpu=0;0, task_cpu(p)=2;2
 ttwu-IPI-self: 2==2, p->on_cpu=0;0, task_cpu(p)=2;2

> Can you also confirm that if you do:
> 
> $ echo NO_TTWU_QUEUE_ON_CPU > /debug/sched_features

With,

 sched_feat_disable(10):TTWU_QUEUE_ON_CPU

the pr_alert is still being hit

 ttwu-IPI-self: 3==3, p->on_cpu=0;0, task_cpu(p)=3;3

At which point, it darns on me. Mea culpa, stray bits being passed into
default_wake_function.

I am very sorry for the wild goose chase.
-Chris

  reply	other threads:[~2020-07-23 19:42 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-22 10:01 [PATCH -v2 0/5] sched: TTWU, IPI and stuff Peter Zijlstra
2020-06-22 10:01 ` [PATCH -v2 1/5] sched: Fix ttwu() race Peter Zijlstra
2020-06-22 12:56   ` Peter Zijlstra
2020-06-23  7:19     ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2020-06-23  8:48     ` [tip: sched/urgent] sched/core: " tip-bot2 for Peter Zijlstra
2020-07-21 10:49   ` [PATCH -v2 1/5] sched: " Chris Wilson
2020-07-21 11:37     ` peterz
2020-07-22  9:57       ` Chris Wilson
2020-07-23 18:28         ` Peter Zijlstra
2020-07-23 19:41           ` Chris Wilson [this message]
2020-07-23 20:11             ` Peter Zijlstra
2020-07-24 17:55               ` Paul E. McKenney
2020-06-22 10:01 ` [PATCH -v2 2/5] sched: s/WF_ON_RQ/WQ_ON_CPU/ Peter Zijlstra
2020-06-23  7:19   ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2020-06-23  8:48   ` [tip: sched/urgent] sched/core: s/WF_ON_RQ/WQ_ON_CPU/ tip-bot2 for Peter Zijlstra
2020-06-22 10:01 ` [PATCH -v2 3/5] smp, irq_work: Continue smp_call_function*() and irq_work*() integration Peter Zijlstra
2020-06-23  7:19   ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2020-06-23  8:48   ` tip-bot2 for Peter Zijlstra
2020-06-22 10:01 ` [PATCH -v2 4/5] irq_work: Cleanup Peter Zijlstra
2020-06-22 10:01 ` [PATCH -v2 5/5] smp: Cleanup smp_call_function*() Peter Zijlstra

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