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From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: mingo@kernel.org, gkohli@codeaurora.org, tglx@linutronix.de,
	mpe@ellerman.id.au, bigeasy@linutronix.de,
	linux-kernel@vger.kernel.org, will.deacon@arm.com
Subject: Re: [PATCH 4/4] kthread: Simplify kthread_park() completion
Date: Tue, 12 Jun 2018 14:42:57 +0200	[thread overview]
Message-ID: <20180612124257.GS12198@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180608095220.GA18941@redhat.com>

On Fri, Jun 08, 2018 at 11:52:20AM +0200, Oleg Nesterov wrote:
> in smpboot_update_cpumask_percpu_thread() can hit a KTHREAD_SHOULD_PARK
> thread? Lets look into kernel test robot's .config:
> 
> 	CONFIG_NR_CPUS=1
> 
> Now look at NR_CPUS==1 version of for_each_cpu* helpers:
> 
> 	#define for_each_cpu(cpu, mask)			\
> 		for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask)

Argh, that issue again.

> So even if the "tmp" cpumask is empty the code above always does
> 
> 		smpboot_park_thread(plug_thread, 0);
> 
> and hits the already parked kthread.

OK, I'll write a new Changelog.

  reply	other threads:[~2018-06-12 12:43 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-07 12:33 [PATCH 0/4] kthread/smpboot: More fixes Peter Zijlstra
2018-06-07 12:33 ` [PATCH 1/4] kthread, sched: Fix kthread_parkme() (again...) Peter Zijlstra
2018-06-07 12:33 ` [PATCH 2/4] watchdog/softlockup: Replace "watchdog/%u" threads with cpu_stop_work Peter Zijlstra
2018-06-07 14:24   ` Peter Zijlstra
2018-06-07 14:42     ` Peter Zijlstra
2018-06-08 13:57     ` Oleg Nesterov
2018-06-12 12:17       ` Peter Zijlstra
2018-06-07 12:33 ` [PATCH 3/4] smpboot: Remove cpumask from the API Peter Zijlstra
2018-06-07 12:33 ` [PATCH 4/4] kthread: Simplify kthread_park() completion Peter Zijlstra
2018-06-08  9:52   ` Oleg Nesterov
2018-06-12 12:42     ` Peter Zijlstra [this message]
2018-06-25  7:12     ` Peter Zijlstra
2018-06-25 16:53       ` Oleg Nesterov

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