linux-kernel - Re: sched: spinlock recursion in sched_rr_get

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Date:	Fri, 26 Dec 2014 02:01:33 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Li Bin <huawei.libin@...wei.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>, rui.xiang@...wei.com,
	wengmeiling.weng@...wei.com
Subject: Re: sched: spinlock recursion in sched_rr_get_interval

On 12/26/2014 01:45 AM, Li Bin wrote:
> On 2014/7/8 4:05, Peter Zijlstra wrote:
>> > On Mon, Jul 07, 2014 at 09:55:43AM -0400, Sasha Levin wrote:
>>> >> I've also had this one, which looks similar:
>>> >>
>>> >> [10375.005884] BUG: spinlock recursion on CPU#0, modprobe/10965
>>> >> [10375.006573]  lock: 0xffff8803a0fd7740, .magic: dead4ead, .owner: modprobe/10965, .owner_cpu: 15
>>> >> [10375.007412] CPU: 0 PID: 10965 Comm: modprobe Tainted: G        W      3.16.0-rc3-next-20140704-sasha-00023-g26c0906-dirty #765
>> > 
>> > Something's fucked; so we have:
>> > 
>> > debug_spin_lock_before()
>> > 	SPIN_BUG_ON(lock->owner == current, "recursion");
>> > 
> Hello，
> Does ACCESS_ONCE() can help this issue? I have no evidence that its lack is
> responsible for the issue, but I think here need it indeed. Is that right?
> 
> SPIN_BUG_ON(ACCESS_ONCE(lock->owner) == current, "recursion");

Could you explain a bit more why do you think it's needed?


Thanks,
Sasha
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