linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Wed, 3 Dec 2014 10:03:56 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	<paulmck@...ux.vnet.ibm.com>
CC:	Dâniel Fraga <fragabr@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: frequent lockups in 3.18rc4

On 12/03/2014 12:58 AM, Dâniel Fraga wrote:
> On Tue, 2 Dec 2014 16:40:37 +0800
> Lai Jiangshan <laijs@...fujitsu.com> wrote:
> 
>> It is needed at lest for testing.
>>
>> CONFIG_TREE_PREEMPT_RCU=y with CONFIG_PREEMPT=n is needed for testing too.
>>
>> Please enable them (or enable them under CONFIG_RCU_TRACE=y)
> 
> 	Lai, sorry but I didn't understand. Do you mean both of them
> enabled? Because how can CONFIG_TREE_PREEMPT_RCU be enabled without
> CONFIG_PREEMPT ?

Sorry, I replied to Paul, and my reply was off-topic, it has nothing
related your reports. Sorry again.

I think we need two combinations for testing (not mainline, but I think
they (combinations) should be enabled for test farms).

So I hope Paul enable them (combinations).

combination1: CONFIG_TREE_PREEMPT_RCU=n & CONFIG_PREEMPT=y
combination2: CONFIG_TREE_PREEMPT_RCU=y & CONFIG_PREEMPT=n

The core code should work correctly in these combinations.
I agree with Paul that these combinations should not be enabled in production,
So my request is: enable these combinations under CONFIG_RCU_TRACE
or CONFIG_TREE_RCU_TRACE.

For myself, I always edit the Kconfig directly, thus it is not a problem
for me.  But there is no way for test farms to test these combinations.

Thanks,
Lai

> 
> 	If you mean both enabled, I already reported a call trace with
> both enabled:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=85941
> 
> 	Please see my previous answer to Linus and Paul too.
> 
> 	Regarding CONFIG_RCU_TRACE, do you mean
> "CONFIG_TREE_RCU_TRACE"? I couldn't find CONFIG_RCU_TRACE.
> 
> 	Thanks.
> 

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