linux-kernel - Re: [PATCH] sched: unify the check on atomic sleeping in __might_sleep() and schedule

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Message-ID: <5051A71C.1070802@linux.vnet.ibm.com>
Date:	Thu, 13 Sep 2012 17:27:56 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	LKML <linux-kernel@...r.kernel.org>
CC:	mingo@...hat.com, Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] sched: unify the check on atomic sleeping in __might_sleep()
 and schedule_bug()

On 09/03/2012 10:16 AM, Michael Wang wrote:
> On 08/22/2012 10:40 AM, Michael Wang wrote:
>> From: Michael Wang <wangyun@...ux.vnet.ibm.com>
>>
>> Fengguang Wu <wfg@...ux.intel.com> has reported 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
>>
>> It was caused by that:
>>
>> 	native_smp_prepare_cpus()
>> 	preempt_disable()		//preempt_count++
>> 	mutex_lock()			//in __irq_alloc_descs
>> 	__might_sleep()			//system is booting, avoid check
>> 	might_resched()
>> 	__schedule()
>> 	preempt_disable()		//preempt_count++
>> 	schedule_bug()			//preempt_count > 1, report bug
>>
>> The __might_sleep() avoid check on atomic sleeping until the system booted
>> while the schedule_bug() doesn't, it's the reason for the bug.
>>
>> This patch will add one additional check in schedule_bug() to avoid check
>> until the system booted, so the check on atomic sleeping will be unified.
> 
> Could I get some comments on this patch?

Oh, I just realised I'm using the wrong address...
So could I get some comments on the patch?

Regards,
Michael Wang

> 
> Regards,
> Michael Wang
>>
>> Signed-off-by: Michael Wang <wangyun@...ux.vnet.ibm.com>
>> Tested-by: Fengguang Wu <wfg@...ux.intel.com>
>> ---
>>  kernel/sched/core.c |    3 ++-
>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 4376c9f..3396c33 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -3321,7 +3321,8 @@ static inline void schedule_debug(struct task_struct *prev)
>>  	 * schedule() atomically, we ignore that path for now.
>>  	 * Otherwise, whine if we are scheduling when we should not be.
>>  	 */
>> -	if (unlikely(in_atomic_preempt_off() && !prev->exit_state))
>> +	if (unlikely(in_atomic_preempt_off() && !prev->exit_state
>> +					&& system_state == SYSTEM_RUNNING))
>>  		__schedule_bug(prev);
>>  	rcu_sleep_check();
>>  
>>
> 

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