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Date: Sat, 06 Oct 2012 17:12:58 +0800
From: Michael Wang <wangyun@linux.vnet.ibm.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: linux-kernel@vger.kernel.org, mingo@redhat.com, svaidy@linux.vnet.ibm.com,
        wfg@linux.intel.com
Subject: Re: [PATCH] sched: fix should_resched() to avoid do schedule in atomic
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On 10/06/2012 05:06 PM, Michael Wang wrote:
> On 09/26/2012 11:41 AM, Michael Wang wrote:
>> On 09/18/2012 11:13 AM, Michael Wang wrote:
>>> This patch try to fix the BUG:
>>>
>>> [    0.043953] BUG: scheduling while atomic: swapper/0/1/0x10000002
>>> [    0.044017] no locks held by swapper/0/1.
>>> [    0.044692] Pid: 1, comm: swapper/0 Not tainted 3.6.0-rc1-00420-gb7aebb9 #34
>>> [    0.045861] Call Trace:
>>> [    0.048071]  [<c106361e>] __schedule_bug+0x5e/0x70
>>> [    0.048890]  [<c1b28701>] __schedule+0x91/0xb10
>>> [    0.049660]  [<c14472ea>] ? vsnprintf+0x33a/0x450
>>> [    0.050444]  [<c1060006>] ? lg_local_lock+0x6/0x70
>>> [    0.051256]  [<c14fb5b1>] ? wait_for_xmitr+0x31/0x90
>>> [    0.052019]  [<c144fd55>] ? do_raw_spin_unlock+0xa5/0xf0
>>> [    0.052903]  [<c1b2a532>] ? _raw_spin_unlock+0x22/0x30
>>> [    0.053759]  [<c105cdbb>] ? up+0x1b/0x70
>>> [    0.054421]  [<c1065d6b>] __cond_resched+0x1b/0x30
>>> [    0.055228]  [<c1b292d5>] _cond_resched+0x45/0x50
>>> [    0.056020]  [<c1b26c58>] mutex_lock_nested+0x28/0x370
>>> [    0.056884]  [<c1034222>] ? console_unlock+0x3a2/0x4e0
>>> [    0.057741]  [<c1ac8559>] __irq_alloc_descs+0x39/0x1c0
>>> [    0.058589]  [<c10223bc>] io_apic_setup_irq_pin+0x2c/0x310
>>> [    0.060042]  [<c20638df>] setup_IO_APIC+0x101/0x744
>>> [    0.060878]  [<c1021d51>] ? clear_IO_APIC+0x31/0x50
>>> [    0.061695]  [<c20600f4>] native_smp_prepare_cpus+0x538/0x680
>>> [    0.062644]  [<c2056a91>] ? do_one_initcall+0x12c/0x12c
>>> [    0.063517]  [<c2056a91>] ? do_one_initcall+0x12c/0x12c
>>> [    0.064016]  [<c2056adc>] kernel_init+0x4b/0x17f
>>> [    0.064790]  [<c2056a91>] ? do_one_initcall+0x12c/0x12c
>>> [    0.065660]  [<c1b2bbd6>] kernel_thread_helper+0x6/0x10
>>>
>>> The process to trigger the BUG is:
>>>
>>> 	native_smp_prepare_cpus()
>>> 	preempt_disable()		//preempt_count++
>>> 	__irq_alloc_descs()
>>> 	mutex_lock()
>>> 	might_sleep()			//should_resched() return true
>>> 	__schedule()
>>> 	preempt_disable()		//preempt_count++
>>> 	schedule_bug()			//preempt_count > 1, report bug
>>>
>>> So the issue is that should_resched() should not return true while the preempt
>>> already disabled.
>>
>> Hi, Peter
>>
>> Could we use this solution to fix the bug?
> 
> Please tell me if it's wrong, I really want to help fix it.

Reset the destination, sorry for the terrible mailing skill...

Regards,
Michael Wang

> 
> Regards,
> Michael Wang
> 
>>
>> Regards,
>> Michael Wang
>>
>>>
>>> This patch will fix the issue, then might_sleep() won't do schedule in atomic
>>> any more.
>>>
>>> Reported-by: Fengguang Wu <wfg@linux.intel.com>
>>> Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
>>> ---
>>>  kernel/sched/core.c |    2 +-
>>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index b38f00e..2b7cd15 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -4171,7 +4171,7 @@ SYSCALL_DEFINE0(sched_yield)
>>>
>>>  static inline int should_resched(void)
>>>  {
>>> -	return need_resched() && !(preempt_count() & PREEMPT_ACTIVE);
>>> +	return need_resched() && !preempt_count();
>>>  }
>>>
>>>  static void __cond_resched(void)
>>>
>>
> 

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