linux-kernel - Re: [PATCH] sched: fix tsk->pi_lock isn't held when do_set_cpus

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Date:	Tue, 25 Aug 2015 16:24:54 +0800
From:	Wanpeng Li <wanpeng.li@...mail.com>
To:	Leo Yan <leo.yan@...aro.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: fix tsk->pi_lock isn't held when
 do_set_cpus_allowed()

On 8/25/15 4:13 PM, Leo Yan wrote:
> Hi Wanpeng,
>
> On Tue, Aug 25, 2015 at 03:59:54PM +0800, Wanpeng Li wrote:
>> [   15.273708] ------------[ cut here ]------------
>> [   15.274097] WARNING: CPU: 0 PID: 13 at kernel/sched/core.c:1156 do_set_cpus_allowed+0x7e/0x80()
>> [   15.274857] Modules linked in:
>> [   15.275101] CPU: 0 PID: 13 Comm: migration/0 Not tainted 4.2.0-rc1-00049-g25834c7 #2
>> [   15.275674]  00000000 00000000 d21f1d24 c19228b2 00000000 d21f1d58 c1056a3b c1ba00e4
>> [   15.276084]  00000000 0000000d c1ba17d8 00000484 c10838be 00000484 c10838be d21e5000
>> [   15.276084]  d2121900 d21e5158 d21f1d68 c1056b12 00000009 00000000 d21f1d7c c10838be
>> [   15.276084] Call Trace:
>> [   15.276084]  [<c19228b2>] dump_stack+0x4b/0x75
>> [   15.276084]  [<c1056a3b>] warn_slowpath_common+0x8b/0xc0
>> [   15.276084]  [<c10838be>] ? do_set_cpus_allowed+0x7e/0x80
>> [   15.276084]  [<c10838be>] ? do_set_cpus_allowed+0x7e/0x80
>> [   15.276084]  [<c1056b12>] warn_slowpath_null+0x22/0x30
>> [   15.276084]  [<c10838be>] do_set_cpus_allowed+0x7e/0x80
>> [   15.276084]  [<c110154c>] cpuset_cpus_allowed_fallback+0x7c/0x170
>> [   15.276084]  [<c11014d0>] ? cpuset_cpus_allowed+0x180/0x180
>> [   15.276084]  [<c1083ae1>] select_fallback_rq+0x221/0x280
>> [   15.276084]  [<c1085073>] migration_call+0xe3/0x250
>> [   15.276084]  [<c1079e23>] notifier_call_chain+0x53/0x70
>> [   15.276084]  [<c1079e5e>] __raw_notifier_call_chain+0x1e/0x30
>> [   15.276084]  [<c1056cc8>] cpu_notify+0x28/0x50
>> [   15.276084]  [<c191e4d2>] take_cpu_down+0x22/0x40
>> [   15.276084]  [<c1102895>] multi_cpu_stop+0xd5/0x140
>> [   15.276084]  [<c11027c0>] ? __stop_cpus+0x80/0x80
>> [   15.276084]  [<c11025cc>] cpu_stopper_thread+0xbc/0x170
>> [   15.276084]  [<c1085ec9>] ? preempt_count_sub+0x9/0x50
>> [   15.276084]  [<c192b6a7>] ? _raw_spin_unlock_irq+0x37/0x50
>> [   15.276084]  [<c192b655>] ? _raw_spin_unlock_irqrestore+0x55/0x70
>> [   15.276084]  [<c10a9074>] ? trace_hardirqs_on_caller+0x144/0x1e0
>> [   15.276084]  [<c11024a5>] ? cpu_stop_should_run+0x35/0x40
>> [   15.276084]  [<c1085ec9>] ? preempt_count_sub+0x9/0x50
>> [   15.276084]  [<c192b641>] ? _raw_spin_unlock_irqrestore+0x41/0x70
>> [   15.276084]  [<c107c944>] smpboot_thread_fn+0x174/0x2f0
>> [   15.276084]  [<c107c7d0>] ? sort_range+0x30/0x30
>> [   15.276084]  [<c1078934>] kthread+0xc4/0xe0
>> [   15.276084]  [<c192c041>] ret_from_kernel_thread+0x21/0x30
>> [   15.276084]  [<c1078870>] ? kthread_create_on_node+0x180/0x180
>> [   15.276084] ---[ end trace 15f4c86d404693b0 ]---
>>
>> After commit (25834c73f93: sched: Fix a race between __kthread_bind()
>> and sched_setaffinity()) do_set_cpus_allowed() should be called w/
>> p->pi_lock held, however, it is not true in cpuset path currently.
>>
>> This patch fix it by holding p->pi_lock in cpuset path.
>>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>>   kernel/cpuset.c |    4 ++++
>>   1 files changed, 4 insertions(+), 0 deletions(-)
>>
>> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
>> index e414ae9..605ed66 100644
>> --- a/kernel/cpuset.c
>> +++ b/kernel/cpuset.c
>> @@ -2376,8 +2376,12 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
>>   
>>   void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
>>   {
>> +	unsigned long flags;
>> +
>>   	rcu_read_lock();
>> +	raw_spin_lock_irqsave(&tsk->pi_lock, flags);
>>   	do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus);
>> +	raw_spin_lock_irqsave(&tsk->pi_lock, flags);
> Just curious, Will introduce deadlock after acquire lock twice? ;)

Could you point out where acquires lock twice?

Regards,
Wanpeng Li

>
> Thanks,
> Leo Yan
>
>>   	rcu_read_unlock();
>>   
>>   	/*
>> -- 
>> 1.7.1
>>
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